Coherent spread-spectrum coded waveforms in synthetic aperture image formation

ABSTRACT

Techniques, systems, and devices are disclosed for synthetic aperture ultrasound imaging using spread-spectrum, wide instantaneous band, coherent, coded waveforms. In one aspect, a method includes synthesizing a composite waveform formed of a plurality of individual orthogonal coded waveforms that are mutually orthogonal to each other, correspond to different frequency bands and including a unique frequency with a corresponding phase; transmitting an acoustic wave based on the composite waveform toward a target from one or more transmitting positions; and receiving at one or more receiving positions acoustic energy returned from at least part of the target corresponding to the transmitted acoustic waveforms, in which the transmitting and receiving positions each include one or both of spatial positions of an array of transducer elements relative to the target and beam phase center positions of the array, and the transmitted acoustic waveforms and the returned acoustic waveforms produce an enlarged effective aperture.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent document is a continuation of and claims priority to U.S.patent application Ser. No. 15/804,955, filed on Nov. 6, 2017, which isa continuation of U.S. patent application Ser. No. 14/479,249, filed onSep. 5, 2014, now U.S. Pat. No. 9,844,359, which claims the benefit ofpriority of U.S. Provisional Patent Application No. 61/877,884, filed onSep. 13, 2013. The entire contents of the before-mentioned patentapplications are incorporated by reference as part of the disclosure ofthis application.

TECHNICAL FIELD

This patent document relates to acoustic image formation.

BACKGROUND

Acoustic imaging is an imaging modality that employs the properties ofsound waves traveling through a medium to render a visual image. Highfrequency acoustic imaging has been used as an imaging modality fordecades in a variety of biomedical fields to view internal structuresand functions of animals and humans. High frequency acoustic waves usedin biomedical imaging may operate in different frequencies, e.g.,between 1 and 20 MHz, or even higher frequencies, and are often termedultrasound waves. Some factors, including inadequate spatial resolutionand tissue differentiation, can lead to less than desirable imagequality using conventional techniques of ultrasound imaging, which canlimit its use for many clinical indications or applications.

SUMMARY

Techniques, systems, and devices are disclosed for synthetic apertureultrasound imaging using coherent, spread-spectrum, instantaneouswideband, frequency- and/or phase-coded acoustic waveforms. Thedisclosed techniques, systems, and devices can be used to formone-dimensional (1D), two-dimensional (2D), and/or three-dimensional(3D) ultrasound images of biological tissue.

The subject matter described in this patent document can provide one ormore of the following features and can be used in many applications. Forexample, the disclosed technology can be used during routine primarycare screenings to identify and locate early-stage pathologies includingmalignancies, as well as later stage cancers, which can potentiallyraise survival rates of hard-to-diagnose asymptomatic patients. Thedisclosed technology can be used by board-certified radiologists todiagnose neoplasms as benign or malignant prior to any surgical biopsyor resection intervention, which may also improve patient survival ratewhile reducing unnecessary biopsies. The disclosed technology, whenintegrated with a fine needle biopsy instrument, can be used in medicalprocedures to confirm noninvasive diagnoses, which can reduce the levelof invasiveness of such biopsy procedures. The disclosed technology,when integrated pre-operatively with Computed Tomography (CT) x-rayimages and/or intra-operatively with minimally invasive surgical highdefinition video instrumentation, can fuse CT, optical and ultrasoundimages, and thereby can further give surgeons added abilities to locate,diagnose, and surgically excise or repair diseased tissue withoutdamaging healthy tissue. The disclosed technology, when integrated withspecialized surgical instrumentation, can fuse ultrasound images withother data, and can give surgeons added abilities to locate andmanipulate anatomic areas of interest while minimizing unnecessarydamage to nearby structures. The disclosed technology can reduce theamount of time for the brachytherapy treatment of malignant neoplasms,for example, by precisely guiding the insertion of sealed radioactivesources and catheters into the proper location. Similarly, the disclosedtechnology can aid insertion of high-dose, localized pharmaceuticals fortreatments of diseases.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a diagram of an ultrasound beam generated by a transducerarray that forms a real aperture beam in ultrasound imaging.

FIG. 1B shows a diagram of an ultrasound beam generated by a transducerarray whose phase center is in successive positions to form a syntheticaperture beam in ultrasound imaging.

FIGS. 1C and 1D show diagrams of exemplary composite ultrasound transmitand/or receive beams generated by a transducer array that forms asynthetic aperture beam from multiple transmitting and/or receivingpositions.

FIG. 1E shows a diagram of an exemplary transducer array for generatinga composite ultrasound beam of the disclosed technology.

FIG. 2A shows a block diagram of an exemplary synthetic apertureultrasound system using spread-spectrum coded waveforms.

FIG. 2B shows a block diagram of another exemplary synthetic apertureultrasound system using spread-spectrum coded waveforms.

FIGS. 2C and 2D show a diagram of exemplary synthetic aperture imagingtechniques of the disclosed technology.

FIG. 2E shows a chart for operation of an exemplary synthetic apertureultrasound imaging system using spread-spectrum coded waveforms.

FIG. 3 shows a graph of an exemplary spread-spectrum, wide instantaneousbandwidth, frequency- and/or phase-coded composite waveform featuring aplurality of waveforms.

FIG. 4 shows ambiguity function characteristics of an exemplaryspread-spectrum coded waveform.

FIGS. 5A-5C show an exemplary diagram for beam steering, dynamicfocusing, and forming.

FIG. 6 shows a block diagram of an exemplary synthetic apertureultrasound signal processing technique to produce an ultrasound image.

FIG. 7 shows a diagram of exemplary synthetic aperture-sampled receivedecho data and storage to memory.

FIG. 8 shows a block diagram of an exemplary wave-number algorithm forwideband, spread-spectrum, noise-like, coherent synthetic aperture imageformation.

FIG. 9 shows a diagram illustrating an exemplary implementation of theStolt Transform process.

FIG. 10 shows a block diagram of an exemplary iterative, closed-loop,synthetic aperture image autofocus subroutine.

DETAILED DESCRIPTION

Ultrasound imaging can be performed by emitting an acoustic waveform(pulse) within a physical elastic medium, which is partly reflected froma boundary between two mediums (e.g., biological tissue structures) andpartially transmitted. The reflection depends on the acoustic impedancedifference between the two mediums (e.g., at the interface between twodifferent biological tissue types). For example, some of the acousticenergy of the transmitted acoustic waveform can be scattered back to thetransducer at the interface to be received, and processed to extractinformation, while the remainder may travel on and to the next medium.In some instances, scattering of the reflection may occur as the resultof two or more impedances contained in the reflective medium acting as ascattering center. Additionally, for example, the acoustic energy can berefracted, diffracted, delayed, and/or attenuated based on theproperties of the medium and/or the nature of the acoustic wave.

In some existing ultrasound imaging systems, a typical transducer mayemploy an array of piezoelectric elements to transmit an ultrasoundpulse toward a target region (e.g., of a body of an organism) andreceive the returned ultrasound signals (echoes) that return fromscattering structures within. This transducer array functions as theaperture of the imaging system. Ultrasound pulses can be electronicallysteered and focused as a sequence pulses through a plane or volume andused to produce a 1D, 2D and/or 3D map of the returned echoes used toform an image of the target. Processes of steering and focusingultrasound pulses is referred to as beamforming. In some examples, theultrasound pulse and the returned echoes transmitted and received at thetransducer array can be individually delayed in time at each transducerof the array to act as a phased array.

In conventional real aperture ultrasound imaging systems, the quality ofimages directly depends on the acoustic field generated by thetransducer of the ultrasound system. FIG. 1A shows a diagram of a realaperture ultrasound beam 111 generated by a transducer array 110, e.g.,which can be configured as a single electro-acoustic transducer elementor an array of multiple electro-acoustic transducer elements of widthw_(R), that forms a real aperture to form the ultrasound beam 111directed toward a volume of interest (VOI) 115. For example, the imageis typically acquired sequentially, one axial image line at a time(i.e., scan of the target area range slice by slice), which sets limitson the frame rate during imaging that may be detrimental in a variety ofreal-time ultrasound imaging applications, e.g., including the imagingof moving targets.

To address limitations with conventional real aperture ultrasoundimaging, synthetic aperture ultrasound imaging can be used to improvethe quality of ultrasound images. A “synthetic aperture” is the conceptin which the successive use of one or more smaller, real apertures(sub-apertures) to examine a VOI, whose phase centers are moved along aknown one-dimensional (1D), two-dimensional (2D), and/orthree-dimensional (3D) path of a particular or arbitrary shape, torealize a larger effective (non-real) aperture for acquiring an image.The synthetic aperture can be formed by mechanically altering thespatial position of the electro-acoustic transducer (e.g., transducerarray) to the successive beam transmission and/or receiving locations,by electronically altering the phase center of the successive beamtransmission and/or receiving locations on the electro-acoustictransducer array, or by a combination of both. Synthetic aperture-basedimaging was originally used in radar systems to image large areas on theground from aircraft scanning the area of interest from above. Syntheticaperture focusing in ultrasound imaging is based on the geometricdistance from the ultrasound transmitting elements to the VOI locationand the distance from that location back to the ultrasound receivingelement. In ultrasound imaging, the use of the synthetic apertureenables the focusing on a point in the target region by analyzing thereceived amplitude and phase data of the returned echoes (e.g.,mono-static and bi-static echoes), recorded at each of a plurality oftransmitter and receiver positions from all directions, to provideinformation about the entire area. Since the direction of the returnedechoes cannot be determined from one receiver channel alone, manyreceiver channels are used to determine the information contained in thereturning echoes, which are processed across some or all of the channelsto ultimately render information used to produce the image of the targetregion.

The synthetic aperture array may be comprised of one or more real beamaperture sub-arrays whose phase center is moved from sampling positionto position, as shown in FIG. 1B. For example, the transducer array maybe composed of multiple real aperture sub-arrays, which together incombination comprise an entire array, with the phase center of one ormore of the sub-arrays moved (e.g., electronically, mechanically, orboth) from sampling position to position.

In one example of a synthetic aperture ultrasound technique, a single ormultiple transducer elements can be used to transmit a divergingwavefront at a plurality of positions across a region containing a VOI,forming an effective aperture covering the full image region. FIG. 1Bshows a diagram of an ultrasound beam generated by transducer arrayswhose phase centers are moved in successive positions to form asynthetic aperture beam in ultrasound imaging. As shown in the diagram,multiple ultrasound beams 121 a, 121 b, . . . 121N are generated by oneor more transducer arrays 110 whose phase center is positionedmechanically, electronically, or both in N successive positions(positions a, b, c, . . . N) along an arbitrary, but known, open orclosed 1D, 2D or 3D path W, which for example, may be a straight line,an arc, a circle, a spiral, or any defined curvilinear path, etc., toform a synthetic aperture for ultrasound imaging of a VOI 125. Thereceived mono-static and bi-static echo signals for all or some of thetransducer elements of the transducer 110 in the effective aperture aresampled for each transmission. For example, the individual receivedultrasound signal data can be used for making a low resolution imagebased on the individual unfocused transmissions, which are subsequentlyprocessed to produce a two-dimensional (2D) and/or three-dimensional(3D) focused image from the individual received ultrasound mono-staticand bi-static echo signals. For example, the use of synthetic apertureultrasound imaging can reduce the system complexity and cost inultrasound imaging, e.g., as compared to a real beam system ofequivalent performance.

The types of waveforms used to generate the acoustic pulse can alsoaffect the quality of images produced in ultrasound imaging. Someconventional ultrasound imaging techniques may use only amplitudeinformation from the reflected signal. For example, when one pulse isemitted, the reflected signal can be sampled continuously. In biologicaltissue, sound velocity can be considered fairly constant (e.g., towithin less than 10%, excluding bone), in which the time between theemission of a waveform and the reception of a reflected signal isdependent on the distance the waveform travels in that tissue structure(e.g., the depth of the reflecting structure). Therefore, reflectedsignals may be sampled at multiple time intervals to receive thereflected signals being reflected from multiple depths. Also, differenttissues at different depths can partially reflect the incident waveformwith different amounts of energy, and thus the reflected signal fromdifferent mediums can have different amplitudes. A correspondingultrasound image can be constructed based on depth. The time before anew waveform is emitted can therefore be dependent of the maximum depththat is desired to image. Ultrasound imaging techniques employing pulsedmonochromatic and/or narrow instantaneous bandwidth waveforms can sufferfrom poor resolution of image processing and production. Yet, waveformswith spread-spectrum, wide instantaneous bandwidth characteristics thatare coded (e.g., by frequency and/or phase) can enable real-time controlof ultrasound imaging and higher quality resultant images.

Disclosed are techniques, systems, and devices for generating,transmitting, receiving, and processing coherent, spread-spectrum,instantaneous-wideband, coded waveforms used in synthetic apertureultrasound (SAU) imaging.

The disclosed SAU imaging techniques can provide improved image quality,contrast and resolution over existing ultrasound imaging techniques andcan enable tissue differentiation and classification. Additionally, theexemplary coherent, spread-spectrum, instantaneous-wideband, codedwaveforms employed in the disclosed technology are not constrained byhardware design limitations currently present in conventional medicalultrasound devices.

The use of coherent waveforms in implementations of the disclosed SAUtechniques can permit the complex correlation of a portion of, or theentire, echo return with a selected reference signal, such as, forexample, the transmitted waveform. Such coherent complex correlationspermit the reduction of image and signal artifacts and the extraction ofdata at lower signal-to-noise ratios and in the presence ofinterference.

The use of spread-spectrum signals in implementations of the disclosedSAU techniques can allow the definitive design of acoustic waveformsthat have deliberate and explicit amplitude and phase frequency content.For example, by explicitly defining the amplitude and/or phase of eachfrequency component of the spread-spectrum composite acoustic waveformscan be constructed such that signal and information processingtechniques can be employed to extract the maximal amount of informationfrom the echo returns, e.g., approaching mathematical limits.

The use of instantaneous coherent, wideband, spread-spectrum, codedwaveforms in implementations of the disclosed SAU techniques can enablethe capture of all available information during each transmit-receiveinterval, e.g., thereby minimizing the corruption of the returned signalby the inhomogeneous, dynamic nature of living biological specimens, andby motion induced artifacts of the collection process. Additionally, forexample, fundamental physical parameters (e.g., such as bulk modulus,density, attenuation, acoustic impedance, amplitude reflections, groupdelay, or other) can be extracted by using signal and informationprocessing methods of the disclosed technology to enable differentiationand classification of the tissue in the VOI. For example, some signaland information processing methods of the disclosed SAU technology mayinclude inverse mathematical techniques operating on the receivedfrequency and angular dependent wideband, spread-spectrum, syntheticaperture received signal echoes for differentiating and/or classifyingtissue in the VOI, as well as expert system techniques, e.g.,deterministic, support vector network and neural network techniques.

Explicit amplitude and/or phase coding of each frequency component ofwaveforms in implementations of the disclosed SAU techniques can providemultiple benefits. For example, amplitude coding allows for the explicitcompensation of the frequency-dispersive properties of the transducerarray and of the acoustic propagation channel. The amplitude and/orphase coding of each frequency component permits deterministicbeamforming and steering of wide-instantaneous waveforms. Explicitamplitude and phase coding of each frequency component of an exemplarytransmitted signal permits the minimization of the peak-to-average powerratio (PAPR), and the spreading of the acoustic power over a wide band,e.g., to minimize deleterious biological effects. For example, byexplicitly defining the amplitude and/or phase of each frequencycomponent of spread-spectrum signals, waveforms can be constructed thatmay be transmitted simultaneously, which exhibit minimal interferencewith each other, such that signal and information processing techniquescan be employed to recover the received signal associated with eachindividual transmitted waveform. Further, the coded, spread-spectrumacoustic waveforms of the disclosed SAU technology can allow for motioncompensation due to particular ambiguity properties of these waveforms.

In one aspect, a method of producing an acoustic waveform in an acousticimaging device is disclosed. The method includes synthesizing, in one ormore waveform synthesizers, one or more composite waveforms formed of aplurality of individual coded waveforms to be transmitted toward atarget from one or more spatial positions of a transducer array of theacoustic imaging device and/or one or more beam phase center positionsof the transducer array. The individual coded waveforms of the compositewaveform are mutually orthogonal to each other and are in differentfrequency bands, such that each of the individual mutually orthogonalcoded waveforms includes a unique frequency with a corresponding phase.The method includes transmitting, from one or more transmittingpositions relative to the target, one or more composite acousticwaveforms formed of a plurality of acoustic waveforms, in which thetransmitting includes selecting one or more transducing elements of anarray to transduce the plurality of individual orthogonal codedwaveforms of the respective one or more composite waveforms into theplurality of corresponding acoustic waveforms of the respective one ormore composite acoustic waveforms. The method includes receiving, at oneor more receiving positions relative to the target, returned acousticwaveforms that are returned from at least part of the targetcorresponding to the transmitted acoustic waveforms, in which thereceiving includes selecting at least some of the transducing elementsof the array to receive the returned acoustic waveforms, and in whichthe receiving positions include one or both of spatial positions of thearray of transducer elements relative to the target and beam phasecenter positions of the array to receive the returned acousticwaveforms. The transmitted acoustic waveforms and the returned acousticwaveforms produce an enlarged effective aperture of the acoustic imagingdevice.

In some implementations, for example, the method includes, intransmitting the acoustic waveforms to the target, controlling thetransducer elements of the array to cause the composite waveforms tochange in orientation with respect to the target so that the targetreceives the acoustic waveforms at different waveform orientations overan imaging period. For example, the change in orientation of thecomposite waveforms with respect to the target can include transmittingdifferent composite waveforms from the same or different spatialpositions, transmitting the same or different composite waveforms fromdifferent spatial positions, and transmitting the same or differentcomposite waveforms from different beam phase center positions on thearray of transducer elements.

In some implementations, for example, the method includes converting thereceived returned acoustic waveforms from analog format to digitalformat as one or more received composite waveforms corresponding to theone or more composite waveforms, each comprising information of thetarget, in which the information includes an amplitude and a phaseassociated with the corresponding frequency bands of the receivedcomposite waveform. Also, in some implementations, for example, themethod can include processing the received returned acoustic waveforms(of the one or more received composite waveforms) to produce an image(e.g., 2D and/or 3D image) of at least part of the target.

In one aspect, a synthetic aperture ultrasound imaging system isdisclosed. The system includes a waveform generation unit including oneor more waveform synthesizers coupled to a waveform generator. Thewaveform generation unit synthesizes a composite waveform that includesa plurality of individual orthogonal coded waveforms corresponding todifferent frequency bands that are generated by the one or more waveformsynthesizers according to waveform information provided by the waveformgenerator, in which the individual orthogonal coded waveforms aremutually orthogonal to each other and correspond to different frequencybands, such that each of the individual orthogonal coded waveformsincludes a unique frequency with a corresponding phase. The systemincludes a transmit/receive switching unit that switches between atransmit mode and a receive mode. The system includes an array oftransducer elements in communication with the transmit/receive switchingunit. The array of transducer elements are configured to transmit acomposite acoustic waveform comprising a plurality of acoustic waveformsfrom one or more transmitting positions relative to the target, in whichthe transmitted acoustic waveforms of the composite acoustic waveformare based on the synthesized individual orthogonal coded waveforms ofthe composite waveform. The array of transducer elements are alsoconfigured to receive, e.g., at one or more receiving positions relativeto the target, returned acoustic waveforms corresponding to theplurality of transmitted acoustic waveforms that return from at leastpart of the target. The transmitted acoustic waveforms and the returnedacoustic waveforms produce an enlarged effective aperture of thesynthetic aperture acoustic waveform imaging system. The transmittingpositions and the receiving positions for transmitting and receiving therespective waveforms, respectively, include one or both of spatialpositions of the array of transducer elements relative to the target andbeam phase center positions on the array to transmit and/or receive theacoustic waveforms. The system includes a multiplexing unit incommunication with the array of transducer elements to select one ormore transducing elements of an array to transduce the plurality ofindividual orthogonal coded waveforms into the plurality ofcorresponding acoustic waveforms, and to select one or more transducingelements of the array to receive the returned acoustic waveforms. Insome implementations, for example, the system includes an array ofanalog to digital (A/D) converters to convert the received returnedacoustic waveforms that are received by the array of transducer elementsfrom analog format to digital format, in which the received returnedacoustic waveforms provide information of the target. The systemincludes a controller unit in communication with the waveform generationunit and the array of transducer elements (e.g., which can be via thearray of A/D converters), in which the controller unit includes a memoryunit to store data and a processing unit coupled to the memory unit toprocess information about the target as data. The system can include auser interface unit in communication with the controller unit. In someimplementations of the system, for example, the controller unit isconfigured to produce an image of at least part of the target from theprocessed data.

FIGS. 1C and 1D show diagrams of exemplary composite ultrasound beamsgenerated by a transducer array that forms a synthetic aperture beamfrom multiple transmitting positions. As shown in the diagram, atransducer array 130 includes multiple real aperture sub-arrays Sub 1,Sub 2, . . . Sub N, in which each sub-array includes individualtransducer elements (e.g., such as 1 to 16, 32, 64, etc. elements). Someor all of the transducer elements that form array 130 can transmit(e.g., either sequentially, simultaneously or randomly) one or morecomposite acoustic waveforms of individual, mutually orthogonal, codedacoustic waveforms 131 a, 131 b, . . . 131 n transmitted to a targetvolume of interest (VOI) 135 from multiple sub-array phase centerpositions to form a synthetic aperture for ultrasound imaging. Some orall of the transducer elements that form the array 130 can also receivethe returned acoustic waveforms corresponding to the transmittedacoustic waveform (formed based on the individual, mutually orthogonal,coded acoustic waveforms 131 a, 131 b, . . . 131 n), in which thereceived acoustic waveforms are scattered back and returned (e.g.,reflected, refracted, diffracted, delayed, and/or attenuated) from atleast part of the VOI 135. The received individual acoustic waveformsthereby form one or more received composite waveforms that correspond tothe transmitted composite acoustic waveforms. The composite acousticwaveform is generated based on a composite synthetic waveform formed ofmultiple spread-spectrum, wide instantaneous bandwidth, coded waveformsused to generate the individual acoustic waveforms. The individual,composite, acoustic waveforms 131 a, 131 b, . . . 131 n can betransducted by one or more of the sub-arrays of the transducer array130. The transducer array 130 can be positioned at multiple physicalpositions along a known path (e.g., shown as position 1 to position 2 inFIG. 1C), and/or multiple beam-steering positions (e.g., shown asposition 1 to position 2 in FIG. 1D), such that the phase center ispositioned mechanically, electronically or both mechanically andelectronically in the successive positions, e.g., forming a syntheticaperture.

In some implementations, for example, various array segments comprisingvarious combinations of transducer elements across one or moresub-arrays can be utilized to generate the orthogonal coded acousticwaveforms 131 a, 131 b, . . . 131 n. FIG. 1E shows a diagram of anexemplary transducer array for generating a composite ultrasound beam ofthe disclosed technology. In the example of FIG. 1E, the transducerarray 130 includes 64 individual transducer elements arranged in fourtransducer segments (e.g., transducer segment 1, 2, 3, and 4). In thisexample, one or more sub-arrays, comprising any of the 64 individualtransducer elements (e.g., including transducer elements among one ormore of the four transducer segments), can transmit (e.g., eithersequentially, simultaneously or randomly) the individual, orthogonal,coded acoustic waveforms 131 a, 131 b, . . . 131 n. A sub-array caninclude combinations of the individual transducer elements in onetransducer segment or among a plurality of the transducer segments. Forexample, a sub-array 1 includes transducer elements 2, 3, 6, 7, 10, 11,14 and 15 of transducer segment 1 and transducer elements 2 and 3 oftransducer segment 3; a sub-array 2 includes transducer elements 1, 2,3, 5, 6, 7, 9, 10, and 11 of transducer segment 2; a sub-array 3includes transducer elements 9, 10, 11, 12, 13, 14, 15, and 16 oftransducer segment 3 and transducer elements 9 and 13 of transducersegment 4; and a sub-array 4 includes transducer elements 5, 6, 7, 9,10, 11, 13, 14, and 15 of transducer segment 4. Configurations of thesub-arrays can be produced using a switching element (e.g., such as amultiplexer unit) interfaced between waveform generators and thetransducer array, as shown later in FIG. 2A and FIG. 2B.

FIG. 2A shows a block diagram of an exemplary Synthetic ApertureUltrasound (SAU) System 200 that can produce acoustic waveforms withenhanced waveform properties across an expanded effective (synthetic)aperture. The enhanced waveform properties of the composite acousticwaveforms produced by the SAU System 200 include a spread-spectrum, wideinstantaneous bandwidth, coherent, pseudo-random noise characteristics,and coding. The SAU System 200 can be configured in one of many systemdesigns. In one example, the SAU System 200 can include a Master Clock201 for time synchronization. The Master Clock 201 can be interfacedwith a System Controller 202, as well as other modules of the SAU System200 operating in temporal synchronization with each other. The SystemController 202 can include a processing unit, e.g., a central processingunit (CPU) of RISC-based or other types of CPU architectures. The SystemController 202 can also include at least one input/output (I/O) unit(s)and/or memory unit(s), which are in communication with the processingunit, to support various functions of the System Controller 202. Forexample, the processing unit can be associated with a system controlbus, e.g., Data & Control Bus 203. The System Controller 202 can beimplemented as one of various data processing architectures, such as apersonal computer (PC), laptop, tablet, and mobile communication devicearchitectures.

The memory unit(s) can store other information and data, such asinstructions, software, values, images, and other data processed orreferenced by the processing unit. Various types of Random Access Memory(RAM) devices, Read Only Memory (ROM) devices, Flash Memory devices, andother suitable storage media can be used to implement storage functionsof the memory unit(s). The memory unit(s) can store pre-stored waveformsand coefficient data and information, which can be used in theimplementation of generating a waveform, e.g., such as aspread-spectrum, wide-instantaneous bandwidth, coherent, pseudo-randomnoise, and frequency and/or phase-coded waveform. The memory unit(s) canstore data and information obtained from received and processedwaveforms, which can be used to generate and transmit new waveforms. Thememory unit(s) can be associated with a system control bus, e.g., Data &Control Bus 203.

The I/O unit(s) can be connected to an external interface, source ofdata storage, and/or display device. The I/O unit(s) can be associatedwith a system control bus, e.g., Data & Control Bus 203. Various typesof wired or wireless interfaces compatible with typical datacommunication standards, such as, but not limited to, Universal SerialBus (USB), IEEE 1394 (FireWire), Bluetooth, IEEE 802.111, Wireless LocalArea Network (WLAN), Wireless Personal Area Network (WPAN), WirelessWide Area Network (WWAN), WiMAX, IEEE 802.16 (Worldwide Interoperabilityfor Microwave Access (WiMAX)), and parallel interfaces, can be used toimplement the I/O unit. The I/O unit can interface with an externalinterface, source of data storage, or display device to retrieve andtransfer data and information that can be processed by the processorunit, stored in the memory unit, or exhibited on an output unit.

The System Controller 202 can control all of the modules of the SAUSystem 200, e.g., through connection via the Data & Control Bus 203. Forexample, the Data & Control Bus 203 can link the System Controller 202to one or more attached digital signal processors, e.g., Digital SignalProcessor 204, for processing waveforms for their functional control.The Digital Signal Processor 204 can include one or many processors,such as but not limited to ASIC (application-specific integratedcircuit), FPGA (field-programmable gate array), DSP (digital signalprocessor), AsAP (asynchronous array of simple processors), and othertypes of data processing architectures. The Data & Control Bus 203 canalso link the System Controller 202, as well as the Digital SignalProcessor 204, to one or more display units with modules for userinterfaces, e.g., Display 205 with a module User Interface 206 toprovide information to a user or operator and to receive input/commandsfrom the user or operator. The Display 205 can include many suitabledisplay units, such as but not limited to cathode ray tube (CRT), lightemitting diode (LED), and liquid crystal display (LCD) monitor and/orscreen as a visual display. The Display 205 can also include varioustypes of display, speaker, or printing interfaces. In other examples,the Display 205 can include other output apparatuses, such as toner,liquid inkjet, solid ink, dye sublimation, inkless (such as thermal orUV) printing apparatuses and various types of audio signal transducerapparatuses. The User Interface 206 can include many suitable interfacesincluding various types of keyboard, mouse, voice command, touch pad,and brain-machine interface apparatuses.

The SAU System 200 can include Waveform Generator 207, which can becontrolled by the System Controller 202 for producing one or moredigital waveforms. The one or more digital waveforms can be generated asanalog electronic signals (e.g., analog waveforms) by at least oneelement in an array of waveform synthesizers and beam controllers, e.g.,represented in this example as Waveform Synthesizer and Beam Controller208. The Waveform Generator 207 can be at least one of a functiongenerator and an arbitrary waveform generator (AWG). For example, theWaveform Generator 207 can be configured as an AWG to generate arbitrarydigital waveforms for the Waveform Synthesizer and Beam Controller 208to synthesize as individual analog waveforms and/or a composite analogwaveform. The Waveform Generator 207 can also include at least onememory unit(s) that can store pre-stored waveforms and coefficient dataand information used in the generation of a digital waveform.

The SAU System 200, as shown in FIG. 2A, includes the WaveformSynthesizer and Beam Controller 208 comprising I number of arrayelements. In one example, the Waveform Synthesizer and Beam Controller208 can be configured to include at least one waveform synthesizerelement on each line of the I number of array waveform synthesizers. Inanother example, the Waveform Synthesizer and Beam Controller 208 caninclude at least one beam controller element on each line of the Inumber of array beam controllers. In another example, the WaveformSynthesizer and Beam Controller 208 can include at least one waveformsynthesizer element and beam controller element on each line of the Inumber of array waveform synthesizers and beam controllers. The WaveformSynthesizer and Beam Controller 208 can include a phase-lock loop systemfor generation of an electronic signal, e.g., a radio frequency (RF)waveform. An exemplary RF waveform can be synthesized by the WaveformSynthesizer and Beam Controller 208 from individual waveforms generatedin the array elements of the Waveform Synthesizer and Beam Controller208, e.g., one individual RF waveform can be generated in one arrayelement substantially simultaneously to all other individual waveformsgenerated by the other array elements of the Waveform Synthesizer andBeam Controller 208. Each individual orthogonal RF waveform can bedefined for a particular frequency band, also referred to as a frequencycomponent or ‘chip’, and the waveform properties of each individualorthogonal waveform can be determined by the Waveform Generator 207,which can include at least one amplitude value and at least one phasevalue corresponding to the chip. The Waveform Generator 207 can issuecommands and send waveform data including information about eachindividual orthogonal waveform's properties to the Waveform Synthesizerand Beam Controller 208 for generation of individual orthogonal RFwaveforms that may be combined together to form a composite RF waveformby the Waveform Synthesizer and Beam Controller 208.

The individual orthogonal RF waveforms and/or the composite RF waveformgenerated by the Waveform Synthesizer and Beam Controller 208 can bemodified by Output Amplifiers 209, which includes an array of I numberof amplifiers, e.g., by amplifying the gain and/or shifting the phase ofa waveform. In some examples, the Output Amplifiers 209 are configuredas linear amplifiers. The Output Amplifiers 209 can be used astransducer drivers. The individual RF waveforms and/or the composite RFwaveform can be passed to Transmit/Receive (T/R) Switch 210, e.g., anN-pole double-throw transmit/receive switch. The T/R Switch 210 can beinterfaced with a transducer module of the SAU System 200. The T/RSwitch 210 can operate as a multiplexing unit, e.g., by including N-polemultiplexing switches. A generated RF waveform, e.g., the composite RFwaveform and/or at least one individual RF waveform, that is to betransmitted into a target medium can be transduced into, for example, anacoustic wave by the transducer module. In the example shown in FIG. 2A,the transducer module is configured as an array of transducer elements,e.g., Transducer Array 211 comprising X number of transducer elements.For example, the transduced acoustic wave can be emitted in the form ofan acoustic waveform burst. For example, selected array element of theTransducer Array 211 may generate (e.g., transduct) two or moreindividual orthogonal acoustic waveforms that correspond to theindividual orthogonal waveforms determined by the Waveform Generator 207and combined spatially to form a composite acoustic waveform. As anadditional example, selected array element of the Transducer Array 211may generate (e.g., transduct) one or more composite acoustic waveformsthat correspond to the composite waveforms determined by the WaveformGenerator 207.

For example, when the T/R Switch 210 is configured in transmit mode, theexemplary transduced and transmitted composite acoustic waveform can betransmitted toward a target area from a plurality of positions of theTransducer Array 211 relative to the target, e.g., biological tissue, inwhich the transduced and transmitted acoustic waveform forms a spatiallycombined acoustic waveform. The transmitted composite acoustic waveformcan propagate into the target medium, which for example, can have one ormore inhomogeneous mediums that partially transmit and partially reflectthe transmitted acoustic waveform. For example, after the acousticwaveform has been transmitted, the T/R Switch 210 can be configured intoreceive mode. The exemplary composite acoustic waveforms that are (atleast partially) reflected by the target can be received by theTransducer Array 211, referred to as returned acoustic waveforms. Insome examples, selected array element of X array elements of TransducerArray 211 can be configured to receive a returned acoustic waveformcorresponding to the individual orthogonal waveforms (e.g., frequencychips) and convert it to an analog RF waveform. In other examples,selected transducer elements of the Transducer Array 211 can beconfigured to receive the returned acoustic waveform corresponding tothe transmitted composite waveform, e.g., based on a selection controlsignal determined by the System Controller 202 in communication withexemplary control logic of the Transducer Array 211, and convert it to acomposite analog RF waveform.

In some implementations, for example, the Transducer Array 211 can havethe beam phase center(s) mechanically translated in one dimension, twodimensions, and/or three dimensions of data sampling/ultrasound scanningpositions by spatially moving the Transducer Array 211 to produce asynthetic aperture during an ultrasound imaging implementation using theSAU System 200. In an additional example, the Transducer Array 211 canremain stationary, and the beam phase center(s) may be translatedelectronically in one dimension, two dimensions, and/or three dimensionsalong the stationary Transducer Array 211 by addressing a portion of theX transducer elements sequentially or randomly by the System Controller202 as data sampling/ultrasound scanning positions to produce asynthetic aperture during an ultrasound imaging implementation using theSAU System 200. As a further example, the SAU System 200 can bothmechanically and electronically translate the phase centers in onedimension, two dimensions, and/or three dimensions of datasampling/ultrasound scanning positions to produce a synthetic apertureduring an ultrasound imaging implementation.

In some implementations, for example, the individual RF waveforms and/orthe composite RF waveform can be passed directly to separatetransmitting transducer arrays, e.g., either separately orsimultaneously in time, and separate receiving transducer arrays can beused to receive the acoustic waveforms scattered from the volume ofinterest. FIG. 2B shows another exemplary embodiment of a syntheticaperture ultrasound system of the disclosed technology in a blockdiagram showing an SAU System 200 a. The SAU System 200 a is operablesimilar to that of the SAU System 200 to produce acoustic waveforms withenhanced waveform properties across an expanded effective (synthetic)aperture, but including: (1) a Transmitter Transducer Array 211 acomprising X number of transducer elements to transduce the I number ofindividual waveforms (e.g., which correspond to the individualorthogonal coded waveform determined by the Waveform Generator 207) andtransmit one or more acoustic waveforms, e.g., either sequentially, orsimultaneously, or randomly in time; and including (2) a separateReceiver Transducer Array 211 b comprising Y number of transducerelements can be configured to receive returned acoustic waveforms, andconvert each to an analog RF waveform. In some examples, X can be equalY, but in other examples, X may not equal Y. In some implementations,the SAU System 200 a can include a T/R Switch 210 a, configured betweenthe Output Amplifiers 209 and the Transmitter Transducer Array 211 a,which can operate as a multiplexing unit, e.g., by including N-polemultiplexing switches. Also, in some implementations, the SAU System 200a can include a T/R Switch 210 b, configured between the ReceiverTransducer Array 211 b and Pre-Amplifier module 212, which can operateas a multiplexing unit, e.g., by including N-pole multiplexing switches.For example, the Transmitter Transducer Array 211 a can transduce the Inumber of individual orthogonal coded waveforms to one or more acousticwaveforms that correspond to RF waveforms determined by the WaveformGenerator 207. The transduced acoustic waveform can be emitted in theform of an acoustic waveform burst. For example, selected array elementsof the Transducer Array 211 a may generate (e.g., transduct) two or moreindividual orthogonal acoustic waveforms that correspond to theindividual orthogonal waveforms determined by the Waveform Generator 207and combined spatially to form one or more composite acoustic waveformsthat are transmitted one or more acoustic waveforms, e.g., eithersequentially, or simultaneously, or randomly in time. As additionalexample, selected array elements of the Transducer Array 211 a maygenerate (e.g., transduct) one or more composite acoustic waveforms thatcorrespond to the composite waveforms determined by the WaveformGenerator 207 that are transmitted either sequentially, orsimultaneously, or randomly in time.

In the exemplary SAU System 200 a, the Transmitter Transducer Array 211a and the Receiver Transducer Array 211 b can have a portion or all oftheir phase centers translated either mechanically, electronically orboth mechanically and electronically in one dimension, two dimensions,and/or three dimensions of data sampling/ultrasound scanning positionsto produce a synthetic aperture during an ultrasound imagingimplementation using the SAU System 200 a. In some implementations, forexample, the X transducer elements of the Transmitter Transducer Array211 a can have a portion or all of their phase centers translated eithermechanically, electronically or both mechanically and electronically inunison in one, two, and/or three dimensions, while in otherimplementations, for example, one or more of the phase centers of Xtransducer elements of the Transmitter Transducer Array 211 a can betranslated either mechanically, electronically or both mechanically andelectronically separately from the other elements of the Array 211 a inone, two, and/or three dimensions. In some implementations, for example,the X or Y transducer elements of the Transducer Array 211 a or 211 b,respectively, can scan (e.g., mechanically, electronically or both) theradiated acoustic beam and the received beam in angle in one and/or twoangular dimensions (e.g., in azimuth and/or elevation). Similarly forexample, in some implementations, the phase centers of Y transducerelements of the Receiver Transducer Array 211 b can be translated (e.g.,mechanically, electronically or both) in unison in one, two, and/orthree dimensions, while in other implementations, one or more of the Ytransducer elements of the Receiver Transducer Array 211 b can betranslated separately from the other elements of the Array 211 b in one,two, and/or three dimensions. For example in one embodiment, each of theX transducer elements of the Transducer Array 211 or 211 a correspondsto one of the I Output Amplifiers 209, e.g., X=I. Alternatively, forexample to reduce the number of components, several groups oftransmitter transducer elements may be formed out of the total of Xtransducer elements and multiplexed together to communicate with lessthan I Output Amplifiers 209 through N-pole multiplexing switches.

Referring to FIGS. 2A and 2B, the individual received (analog) RFwaveforms can be modified by Pre-Amplifier Module 212, which includes anarray of J or a fewer number of amplifiers, which in someimplementations, for example, each amplifier in the array may correspondto each of the X or Y transducer elements of the Transducer Array 211 orReceiver Transducer Array 211 b, respectively. Alternatively, forexample, to reduce the number of components, several groups of receivertransducer elements may be formed out of the total of receivertransducer elements and multiplexed together to communicate with thepre-amplifiers through N-pole multiplexing switches. For example, eachof the corresponding amplifiers of the Pre-Amplifier Module 212 or atleast some of the amplifiers can amplify the gain and/or shifting thephase of the individual received (analog) RF waveform. In some examples,the array of J amplifiers of the Pre-Amplifier Module 212 are configuredas linear amplifiers. In some examples, the Pre-Amplifier Module 212 canbe implemented to perform other signal conditioning techniques to thereceived waveforms. After amplification and/or signal conditioning, forexample, the individual received waveforms can be converted from analogformat to digital format by analog to digital (A/D) Converter Module213, which includes an array of J number of A/D converters. The A/DConverter Module 213 can include A/D converters that have low leastsignificant bit (LSB) jitter, spurious-free dynamic range (SFDR) andwaveform dependency, such that the exemplary waveforms can be adequatelydecoded. The converted digital representations of the individualreceived waveforms can be processed by a processor, e.g., the DigitalSignal Processor 204, in manner that creates and forms a representativeimage of the target medium.

The SAU System 200 can be operated in one of many operation modes. Inone example, the Master Clock 201 can provide the time base forsynchronizing the modules of the SAU System 200, e.g., including theWaveform Generator 207, the Waveform Synthesizers 208, and the DSP 204.The Master Clock 201 can be configured as a low-phase noise clock suchthat the exemplary waveforms can be phase encoded. An operator canselect synthetic aperture modes of operation at the User Interface 206.In some implementations of the SAU System 200, the synthetic aperturemodes can include, but is not limited to, a synthetic aperture stripscan (SASS) mode and an exemplary synthetic aperture spotlight (SASpl)mode.

FIGS. 2C and 2D respectively show diagrams of the exemplary SASS modeand the exemplary SASpl mode of the disclosed technology. As shown inFIG. 2C, for example, the SASS mode is operable to produce a syntheticaperture based on multiple acoustic waveforms transmitted from aplurality of positions about the target via electronic, mechanical, or acombination of both electronic and mechanical translational movement ofthe phase center of the Transducer Array 211 in one, two, and/or threedimensions. As shown in FIG. 2D, for example, the SASpl mode is operableto steer the transmit and/or receive beams to remain centered on theVOI, e.g., thus producing a larger synthetic aperture than the SASSmode, which correspondingly produces finer lateral image resolution. TheSASS and SASpl exemplary modes of operations can include 2D planar sliceand/or 3D volume tomographic renderings, which can be manipulated by anoperator, e.g., using the SAU System 200, to provide sagittal, coronal,transverse or any arbitrary plane of view. An operator can also selectreal aperture modes of operation.

For example, some exemplary modes of operation provided for the user toselect at the User Interface 206 can include conventional A-Mode (e.g.,1D depth-only image), conventional B-Mode (e.g., 2D planerimage—transverse vs. depth), conventional C-Mode (e.g., 2D planer imageat selected depth), conventional D-Modes (e.g., Doppler Modes), and HighIntensity Focused Ultrasound (HIFU) as an integrated surgicaltherapeutic mode combined with any one or more of the conventional ornew modes of operation. Exemplary Doppler modes include Color Doppler(e.g., superposition of color coded Doppler and B-mode images),Continuous Doppler (e.g., 1D Doppler profile vs. depth), Pulsed WaveDoppler (e.g., Doppler vs. time for selected volume), and Duplex/TriplexDoppler (e.g., superposition of conventional B-Mode, conventional C-Modeor Color Doppler, and Pulsed Wave Doppler). The exemplary SAU System 200can additionally implement new modes of operation that can generatespread-spectrum, wide-instantaneous bandwidth, frequency- and/orphase-coded waveforms. For example, a user can select a high-definition2D image mode that is similar to the conventional B-Mode, but hassignificantly better image quality (e.g., higher resolution, contrastratio, etc.), or the user can select a high-definition 3D imaging modethat produces volumetric images that can be displayed as userselectable, 2D images in a manner similar to CT and Magnetic ResonanceImaging (MRI) modalities. Additionally, for example, a user can selectexemplary ATS-Modes (Artificial Tissue Staining Modes) that can comprisea B-Mode, a C-Mode, a D-Mode, or other mode combined with image colorcoding to aid tissue differentiation—analogous to tissue staining formicroscopic histological studies; and exemplary CAD-Modes (ComputerAided Diagnostic Modes) that differentiate and identify tissue type.ATS-Modes can employ the use of features for image color coding in imageprocessing based on one or more of a number of measured properties thatare obtained from the returned echo waveform from the target area, e.g.,the returned echo from an exemplary transmitted spread-spectrum, wideinstantaneous bandwidth, coded acoustic waveform. CAD-Modes can useclassifiers (algorithms) to classify, for example, tissue types based onfeatures of the measured properties of the returned echoes from thetarget area, e.g., the returned echoes from an exemplaryspread-spectrum, wide instantaneous bandwidth, coded, angularly diverse,mono-static and bi-static, synthetic aperture acoustic waveforms. Thefeatures properties can include differing impedances, waveformreflections (as a function of wavelength), group delay, etc. Someexemplary classifiers that can be employed using CAD-Modes can includedeterministic classifiers, stochastic classifiers (e.g., Bayesian andSupport Vector Network classifiers), and neural network classifiers.

FIG. 2E shows an exemplary operation method 250 for operating the SAUSystem 200 or 200 a for synthetic aperture ultrasound imaging. For eachtime epoch, the method 250 can begin by implementing a process 251 tocheck a user-defined mode of operation. For example, mode of operationcan be selected by a user using the User Interface 206, or the mode ofoperation can be selected by another entity or internally within the SAUSystem 200 or 200 a. Based on the selected operation mode, the SystemController 202 can command the Waveform Generator 207 to issue a digitalmessage (data) to one or more elements in the Waveform Synthesizers andBeam Controllers 208 that defines the frequency, amplitude and phase ofeach of the frequency chips that form a desired wideband composite RFwaveform commanded, e.g., implemented in a process 252. The process 251can occur anywhere and implemented in multiple instances during themethod 250. The method 250 includes a process 252 to issue waveform data(e.g., the exemplary digital message/data) to waveform synthesizers andbeamformers, such as the Waveform Synthesizers and Beam Controllers 208.The issued waveform data can include the frequency, amplitude and phaseinformation of the desired frequency chips that are synthesized as theorthogonal frequency- and/or phase-coded waveforms, in which each codedwaveform corresponds to a distinct frequency band. The method 250includes a process 253 to enable transmit mode of the SAU System 200 or200 a. For example, when implementing the SAU System 200, the process253 can switch the SAU System 200 in transmit mode by utilizing theSystem Controller 202 to command an N-pole double-throw T/R switch,e.g., T/R Switch 210, to transmit position. The process 253 can beimplemented in multiple instances during the method 250, e.g., such asafter receiving returned echo signals in a process 258, as describedlater. The method 250 includes a process 254 to generate individualanalog RF waveforms that correspond to defined frequency chips. Forexample, each element in the array of Waveform Synthesizers and BeamControllers 208 can convert the digital message/data from the WaveformGenerator 207 into individual analog waveforms that can make up acoherent analog wideband composite waveform. In some implementations,the method 250 can include a process 255 to amplify the individualanalog waveforms that can make up a coherent analog wideband compositewaveform. For example, each analog waveform and/or wideband compositewaveform can be amplified by an array element in the Output Amplifier209. The amplified analog wideband composite waveform can then passthrough the T/R Switch 210 and excite its respective array element ofthe Transducer Array 211, e.g., in an ultrasound probe. The method 250includes a process 256 to transduce the composite analog waveform to anacoustic waveform that can propagate throughout the scanned volume. Forexample, each element of the Transducer Array 211 can provide anacoustic waveform from each of the individual analog waveformcorresponding to the frequency chip generated in the WaveformSynthesizer and Beam Controller 208 that makes up the wideband compositeacoustic waveform. The Transducer Array 211 can form the acoustic beamthat propagates into the target medium, e.g., biological tissue volumeunder study. At the end of the process 256, the method 250 can implementa process 257 to enable receive mode of the SAU System 200 or 200 a. Forexample, when implementing the SAU System 200, the process 257 canswitch the SAU System 200 in receive mode by utilizing the SystemController 202 to command the N-pole double-throw T/R Switch 210 toreceive position. The method 250 includes a process 258 to receive areturned acoustic waveform, which can be in the form of one or morereturned acoustic waveforms. The process 258 can also includetransducing the returned acoustic waveform echo(es) into individualreceived analog waveforms, e.g., corresponding to the frequency chips ofthe generated individual waveforms. For example, the returned acousticwaveform propagates back to and is received by Transducer Array 211.Each element of Transducer Array 211 can convert the received acousticwaveform it receives into an analog signal (waveform).

In some implementations of the method 250, the Transducer Array 211 canbe translated to another position relative to the target. The processes253-258 can be repeated for each of a plurality of positions of theTransducer Array 211 about the target to form a synthetic aperture, asexemplified in FIG. 2C. In some implementations of the method 250, theTransducer Array 211 can be used to steer the transmitted acousticwaveforms transmitted from one or more positions of the plurality ofpositions, e.g., which can be at one or more of the correspondingtransducer elements of the Transducer Array 211, to form the syntheticaperture, as exemplified in FIG. 2D. For example, the transmittedacoustic waveforms can be steered based on the produced syntheticaperture image, at one or more positions of the plurality of positionsin a direct path toward the target. Also, for example, the SystemController 202 can generate for each waveform of the plurality of codedwaveforms a plurality of amplitudes and a plurality of phases that areindividually amplitude weighted and individually phase weighted,respectively, thereby providing the steering of the acoustic waveformfrom the position toward the target.

In some implementations, the method 250 can include a process 259 toamplify the individual received analog waveforms. For example, eachreceived analog waveform can be amplified by its respective low noisepre-amplifier element in Pre-Amplifier Module 212. The method 250includes a process 260 to convert the individual received analogwaveforms into digital waveform data. For example, each received (andamplified) analog waveform signal can be converted into a digital wordby each respective A/D element in A/D Converter module 213. The digitalformat data can be sent to the Digital Signal Processor 204 for signalprocessing.

The method 250 includes a process 261 to process the digital waveformdata into a synthetic aperture image and image frames representative ofthe target medium. The process 261 is explained further detail later inFIG. 6. The process 261 can also include compositing the digitalwaveform data into a composite digital signal representing theindividual and composite received analog waveform. For example, theDigital Signal Processor 204 can detect the amplitude and phase of eachof the frequency chips that comprise the wideband composite acousticwaveform received by each of the transducer array elements for thesynthetic aperture. The Digital Signal Processor 204 can form thereceived beam and separate the amplitude and Doppler components of eachresolution element of the beam, and can form an image frame associatedwith mode previously selected by operator. The image frame formed by theDigital Signal Processor 204 can be displayed on Display 205 to theuser.

The SAU System 200 can be implemented to produce spread-spectrum, wideinstantaneous bandwidth (e.g., up to 100% or more of fractionalbandwidth), coherent, pseudo-random noise (PRN), frequency- and/orphase-coded waveforms for ultrasound imaging. There are limitlessembodiments of such waveforms. One example is featured in FIG. 3, whichshows an exemplary plot of a generated Composite Waveform 300 that iscomprised of a plurality of individual waveforms (e.g., frequencychips). In some implementations, the individual waveforms of theComposite Waveform 300 can be PRN waveforms including a sequence ofpulses for each frequency chip that repeats itself after a sequence orcode period (T), e.g., such that the sequence has a very low correlationwith any other sequence in the set of frequency chips, or with the samesequence at a significantly different time frame, or with narrow bandinterference or thermal noise. For example, the SAU System 200 cangenerate exactly the same sequences of the exemplary PRN waveforms atboth the transmitter and the receiver ends, so a received signalsequence (based on the transmitted signal sequence) can exhibit a highcorrelation for signal processing to produce an acoustic image of thetarget.

As shown in FIG. 3, an exemplary individual waveform or Chip 301 of theComposite Waveform 300 corresponds to the frequency chip f_(N−2) that istransmitted during a transmit period T beginning at time frame t₀, e.g.,as described in the process 256 in FIG. 2E. As shown in FIG. 3,following the transmit period T, a receive time interval T_(R) isexhibited, in which returned acoustic waveform echoes are received asdescribed in the process 258 in FIG. 2E. The transmit period T and thereceive time interval T_(R) form a frame period T_(f), which can berepeated in subsequent time frames (t₁, t₂, t₃, . . . ).

The exemplary Composite Waveform 300 can be represented by an equationfor waveform, W, which can be represented in the time domain as acomplex number, given by Equation (1):

$\begin{matrix}{{W(t)} = {\sum\limits_{k}{\sum\limits_{n}^{M}{A_{n}e^{j{({{2\;\pi\;{nf}_{0}t} + \Phi_{nk} + C_{n}})}}{U\left( {t - {kT}_{f}} \right)}}}}} & (1)\end{matrix}$

W is comprised of M individual orthogonal waveforms (e.g., orthogonalfrequency chips), where j=−√{square root over (−1)}. In Equation (1), nrepresents the number of frequency chips in the composite waveform W; krepresents the number of changes in time (e.g., frames); T representsthe chip duration or period of the coded sequence; and f₀ represents thefundamental chip frequency, such that f₀=1/NT, and in which Nf₀ is themaximum frequency and (M−N+1)f₀ is the minimum frequency. For example,the number of frequency chips n represents a sequence of positiveintegers from N−M+1 to N. The waveform repetition frequency is 1/T_(f),with T_(f) being the duration of a frame or epoch, and U(x)=1 for0≤x≤T_(f). Φ_(nk) represents the frequency chip phase term of the n^(th)chip in the k^(th) time epoch, and A_(n) is the amplitude of the n^(th)chip. For example, the frequency chip phase term Φ_(nk) can be apseudo-random phase term, in which a pseudo-randomly scrambled startingphase Φ_(nk) is a random number in the set {I_(nk)2π/N}, where Ink is asequence of random, positive integers selected without replacement fromthe series I=0, 1, 2, 3, . . . , N, with N being a large number. Inanother example, the frequency chip phase term Φ_(nk) can be selectedusing any one of a number of numerical techniques to produce sets ofwaveforms W_(s)(t) that are statistically orthogonal to each other tothe degree desired. C_(n), which is an additive phase term, is a numberbetween 0 and 2π. For example, the frequency chip phase pseudo-randomvalues Φ_(nk) can be pre-stored in an exemplary database within a memoryunit of System Controller 202 and/or Waveform Generator 207.

The composite waveform, W, can be formed by synthesizing individual,substantially orthogonal, coded waveforms (e.g., frequency chips), inwhich each individual coded waveform corresponds to a distinct frequencyband, and the coded waveforms includes at least one of frequency-codedwaveforms or phase-coded waveforms, e.g., the coded waveformssynthesized in the Waveform Synthesizers 208. The composite codedwaveforms can be synthesized as frequency-coded waveforms by selectingtwo or more frequencies that define the carrier frequencies of thefrequency chips (e.g., including selecting the minimum and maximumfrequency) and determining the A_(n) amplitude values of the frequencychips. The synthesis of the frequency-coded waveforms can also includedetermining a time-bandwidth product (Mf₀T) parameter of each waveformof the coded waveforms. In some implementations, the amplitude for aparticular frequency chip can be determined as a single value for thatfrequency chip during a particular time epoch and repeated in subsequenttime epochs for the particular frequency chip. In other implementations,the amplitude for a particular frequency chip can be determined as asingle value for that frequency chip during a particular time epoch andassigned a different single value in subsequent time epochs for theparticular frequency chip. And in other implementations, the amplitudefor a particular frequency chip can be determined to include multipleamplitude values for that frequency chip during a particular time epoch,in which the multiple values of the A_(n) can be repeated or varied insubsequent time epochs for the particular frequency chip. The selectionof the range of frequencies from the maximum frequency (Nf₀) to theminimum frequency ((M−N+1)f₀) plus the set of individual waveformamplitude terms (A_(n)) can utilize one of many known code sequences(e.g. including pushing sequences, Barker Codes, etc.) or, for example,utilize a numerical search on pseudo-random codes or any other codes forminimum ambiguity sidelobes.

The composite coded waveforms can additionally or alternatively besynthesized as phase-coded waveforms by determining individual waveformphase terms (Φ_(nk)) of each waveform of the individual coded,orthogonal waveforms (e.g., frequency chips). For example, to providevariation of the composite waveform, W, the phase Φ_(nk) can include oneor more phase values for a frequency chip within the transmit period T.In some implementations, the phase Φ_(nk) for a particular frequencychip can be determined as a single value for that frequency chip duringa particular time epoch and repeated in subsequent time epochs for theparticular frequency chip. In other implementations, the phase Φ_(nk)for a particular frequency chip can be determined as a single value forthat frequency chip during a particular time epoch and assigned adifferent single value in subsequent time epochs for the particularfrequency chip. And in other implementations, the phase Φ_(nk) for aparticular frequency chip can be determined to include multiple valuesfor that frequency chip during a particular time epoch, in which themultiple values of the Φ_(nk) can be repeated or varied in subsequenttime epochs for the particular frequency chip. For example, the waveform301 in the first time epoch (t₀) can include a first phase Φ_(A), forexample, as its phase shift for the beginning portion of the transmitperiod T and a second phase Φ_(B), for example, as its phase shift forthe latter portion of the transmit period T. The waveform 301 in thenext time epoch (t₁) can repeat the exemplary phases Φ_(A) and Φ_(B) asits beginning and latter phase shifts or include another phase shiftsequence (e.g., such as Φ_(A), Φ_(B), Φ_(C), or such as Φ_(B) and Φ_(A),or other configurations). The synthesis of the frequency-coded can alsoinclude determining a time-bandwidth product (Mf₀T) parameter of eachwaveform of the coded waveforms.

An exemplary transmitted composite waveform, W, can be comprised of theset of M individual waveforms that are orthogonal and completely spanthe frequency range f_(N−M+1) to f_(N), as shown in FIG. 3. Theparameter N can be chosen to be a large number to give W a wideinstantaneous bandwidth. In the special case when the lowest frequencyf_(N−M+1)=1/T, then W can describe any wideband waveform that may becontained within this range of frequencies. For any waveform among the Mindividual waveforms, one or more phases (e.g., Φ_(nk)) can be encodedin a single waveform during the interval T. Additionally, any waveformamong the M individual waveforms can include multiple amplitudes encodedin a single waveform. This can be implemented by amplitude weighting andphase weighting.

The family of individual, mutually orthogonal, waveform chips describedby Equation (1) can form a coherent, pseudo-random noise, frequency-and/or phase-coded, spread-spectrum composite waveform. Based on theselection of parameters, the individual waveforms can be made to bestatistically orthogonal to each other, to any degree desired. Forexample, the delay and frequency sidelobe levels of the ambiguityfunction, described in Equation (2), for a given waveform represents thedegree of orthogonality of that waveform. By determining particularparameters of the waveforms, medical ultrasound image resolution can besignificantly improved. For example, parameters that affect theresolution of medical ultrasound images include the time-bandwidthproduct (Mf₀T) parameter, which determines the inherent combined axialrange (e.g., Doppler resolution) and the speckle reduction ability ofthe waveform, and the individual waveform phase terms (Φ_(nk)), whichdetermine the statistical degree of orthogonality, e.g., which in turndetermines the degree that the waveform can function in inhomogeneousmedia of biological tissues. For example, the lower the sidelobes, thegreater the orthogonality and greater the resolution (less noise). Theselection of the set of individual waveform phase terms (Φ_(nk)) canutilize one of many known code sequences (e.g. including Barker, Frank,Golay, etc.) or, for example, utilize a numerical search onpseudo-random codes or any other codes for minimum ambiguity sidelobes.

In some implementations, the Composite Waveform 300, described byEquation (1), which for example can be a single-wideband, coherent,frequency- and/or phase-coded waveform. For example, based on theselection of parameters, the single waveform can be made to bestatistically orthogonal to any other signal waveform or noise signalpresent in the target medium.

The parameter A_(n), which is the amplitude of the n^(th) chip, andC_(n), which is an additive phase term, in combination can providepre-emphasis of the analog signal that excites each individual elementof Transducer Array 211 to produce a transmitted acoustic waveform thathas the desired amplitude and phase characteristics over the frequencyrange of W. Pre-emphasis of the transmitted waveform can compensate forboth the non-constant amplitude and phase response of transducerelements as a function of frequency, and the non-uniform propagationcharacteristics of intervening tissue layers. For example, thepre-emphasis terms can provide an acoustic waveform that has equalamplitude chips with constant (e.g., flat) amplitude and a known phaseversus frequency characteristic. Such constant amplitude versusfrequency acoustic waveforms can be referred to as ‘white’ waveforms.Alternatively, if pre-emphasis is not provided, then the transmittedacoustic waveform can replicate the frequency response of thetransducer, and such waveforms are referred to as ‘colored’ waveforms.De-emphasis of the received waveform can permit determination of thereflection characteristic of the target medium's volume, e.g.,biological tissue volume.

The composite waveform W, as described by Equation (1), is an aggregateof two or more individual, mutually orthogonal, coded waveforms, whichalso may be referred to as chips. Each individual, mutually orthogonal,coded waveform of the composite waveform has a unique frequency with acorresponding specific phase that is associated with each uniquefrequency. In some implementations, the individual, mutually orthogonal,coded waveforms can be amplitude- and phase-coded, where each uniquefrequency waveform includes a corresponding specific phase and amplitudeassociated with each unique frequency. In implementations, for example,the individual, mutually orthogonal, coded waveforms of the compositewaveform W can be transmitted sequentially or simultaneously transmittedtoward a target, or in some implementations, can be randomly transmittedtoward the target.

In one illustrative example, a composite waveform W₁ includes fiveindividual coded waveforms orthogonal to one another: a first waveformcomprising a frequency f₁ with a corresponding specific phase φ₁, asecond waveform comprising a frequency f₂ with a corresponding specificphase φ₂, a third waveform comprising a frequency f₃ with acorresponding specific phase φ₃, a fourth waveform comprising afrequency f₄ with a corresponding specific phase φ₄, and a fifthwaveform comprising a frequency f₅ with a corresponding specific phaseφ₅, which can be represented as:W ₁ =f ₁,φ₁ +f ₂,φ₂ +f ₃,φ₃ +f ₄,Φ₄ +f ₅,φ₅.Similarly, for example, a composite waveform W₂ having five individualorthogonal coded waveforms can include a first waveform comprising afrequency f₁ with a corresponding specific phase φ₆, a second waveformcomprising a frequency f₂ with a corresponding specific phase φ₇, athird waveform comprising a frequency f₃ with a corresponding specificphase φ₈, a fourth waveform comprising a frequency f₄ with acorresponding specific phase φ₉, and a fifth waveform comprising afrequency f₅ with a corresponding specific phase φ₁₀, which can berepresented as:W ₂ =f ₁,φ₆ +f ₂,φ₇ +f ₃,φ₈ +f ₄,φ₉ +f ₅,φ₁₀.Similarly, for example, a composite waveform W₃ having five individualorthogonal coded waveforms can include a first waveform comprising afrequency f₆ with a corresponding specific phase φ₆, a second waveformcomprising a frequency f₇ with a corresponding specific phase φ₇, athird waveform comprising a frequency f₈ with a corresponding specificphase φ₈, a fourth waveform comprising a frequency f₉ with acorresponding specific phase φ₉, and a fifth waveform comprising afrequency f₁₀ with a corresponding specific phase φ₁₀, which can berepresented as:W ₃ =f ₆,φ₆ +f ₇,φ₇ +f ₈,φ₈ +f ₉,φ₉ +f ₁₀,φ₁₀.Similarly, for example, a composite waveform W₄ having five individualorthogonal coded waveforms can include a first waveform (e.g., same asthe first waveform in W₁) comprising the frequency f₁ with acorresponding specific phase φ₁, a second waveform (e.g., same as thesecond waveform in W₁) comprising a frequency f₂ with a correspondingspecific phase φ₂, a third waveform comprising a frequency f₈ with acorresponding specific phase φ₁₁, a fourth waveform (e.g., same as thethird waveform in W₂) comprising the frequency f₃ with a correspondingspecific phase φ₈, and a fifth waveform (e.g., same as the fifthwaveform in W₃) comprising the frequency f₁₀ with a correspondingspecific phase φ₁₀, which can be represented as:W ₄ =f ₁,φ₁ +f ₂,φ₂ +f ₈,φ₁₁ +f ₃,φ₈ +f ₁₀,φ₁₀.Similarly, for example, a composite waveform W₅ having five individualorthogonal coded waveforms can include a first waveform comprising thefrequency f₁ with a corresponding specific phase φ₁₂, a second waveformcomprising a frequency f₂ with a corresponding specific phase φ₁₂, athird waveform comprising a frequency f₈ with a corresponding specificphase φ₁₂, a fourth waveform comprising the frequency f₃ with acorresponding specific phase φ₁₂, and a fifth waveform (e.g., same asthe fifth waveform in W₃) comprising the frequency f₁₀ with acorresponding specific phase φ₁₀, which can be represented as:W ₅ =f ₁,φ₁₂ +f ₂,φ₁₂ +f ₈,φ₁₂ +f ₃,φ₁₂ +f ₁₀,φ₁₀.All of these exemplary composite waveforms (W₁, W₂, W₃, W₄, W₅) in thisexample can be orthogonal to each other or can be designed to have aslow of a cross-correlation as desired.

In another illustrative example, a composite waveform W₆ includes fiveindividual coded waveforms orthogonal to one another: a first waveformcomprising a frequency f₁ with a corresponding specific phase φ₁ andamplitude A₁, a second waveform comprising a frequency f₂ with acorresponding specific phase φ₂ and amplitude A₂, a third waveformcomprising a frequency f₃ with a corresponding specific phase φ₃ andamplitude A₃, a fourth waveform comprising a frequency f₄ with acorresponding specific phase φ₄ and amplitude A₄, and a fifth waveformcomprising a frequency f₅ with a corresponding specific phase φ₅ andamplitude A₅, which can be represented as:W ₆=(f ₁,φ₁ ,A ₁)+(f ₂,φ₂ ,A ₂)+(f ₃,φ₃ ,A ₃)(f ₄,φ₄ ,A ₄)+(f ₅,φ₅ ,A₅).Similarly, for example, a composite waveform W₇ having five individualorthogonal coded waveforms can include a first waveform comprising afrequency f₁ with a corresponding specific phase φ₆ and amplitude A₆, asecond waveform comprising a frequency f₂ with a corresponding specificphase φ₇ and amplitude A₇, a third waveform comprising a frequency f₃with a corresponding specific phase φ₈ and amplitude A₈, a fourthwaveform comprising a frequency f₄ with a corresponding specific phaseφ₉ and amplitude A₉, and a fifth waveform comprising a frequency f₅ witha corresponding specific phase φ₁₀ and amplitude A₁₀, which can berepresented as:W ₇=(f ₁,φ₆ ,A ₆)+(f ₂,φ₇ ,A ₇)+(f ₃,φ₈ ,A ₈)(f ₄,φ₉ ,A ₉)+(f ₅,φ₁₀ ,A₁₀).

Similarly, for example, a composite waveform W₈ having five individualorthogonal coded waveforms can include a first waveform comprising afrequency f₆ with a corresponding specific phase φ₆ and amplitude A₆, asecond waveform comprising a frequency f₇ with a corresponding specificphase φ₇ and amplitude A₇, a third waveform comprising a frequency f₈with a specific phase φ₈ and amplitude A₈, a fourth waveform comprisinga frequency f₉ with a corresponding specific phase φ₉ and amplitude A₉,and a fifth waveform comprising a frequency f₁₀ with a correspondingspecific phase φ₁₀ and amplitude A₁₀, which can be represented as:W ₈=(f ₆,φ₆ ,A ₆)+(f ₇,φ₇ ,A ₇)+(f ₈,φ₈ ,A ₈)(f ₉,φ₉ ,A ₉)+(f ₁₀,φ₁₀ ,A₁₀).Similarly, for example, a composite waveform W₉ having five individualorthogonal coded waveforms can include a first waveform (e.g., same asthe first waveform in W₆) comprising the frequency f₁ with acorresponding specific phase φ₁ and amplitude A₁, a second waveform(e.g., same as the second waveform in W₆) comprising a frequency f₂ witha corresponding specific phase φ₂ and amplitude A₂, a third waveformcomprising a frequency f₈ with a corresponding specific phase cell andamplitude A₁₁, a fourth waveform (e.g., same as the third waveform inW₇) comprising the frequency f₃ with a corresponding specific phase φ₈and amplitude A₈, and a fifth waveform (e.g., same as the fifth waveformin W₈) comprising the frequency f₁₀ with a corresponding specific phaseφ₁₀ and amplitude A₁₀, which can be represented as:W ₉=(f ₁,φ₁ ,A ₁)+(f ₂,φ₂ ,A ₂)+(f ₈,φ₁₁ ,A ₁₁)(f ₃,φ₈ ,A ₈)+(f ₁₀,φ₁₀,A ₁₀).All of these exemplary composite waveforms (W₆, W₇, W₈, W₉) in thisexample can be orthogonal to each other or can be designed to have aslow of a cross-correlation as desired.

By inspection, single frequency modes (e.g., Conventional A-, B- andC-Mode), due to their monochromatic nature, do not need pre-emphasis.Such single frequency waveforms may require amplitude control, forexample, to ensure biologically safe sound intensity limits.

If the phase of each chip is random, the transmitted waveform, W, canhave random noise-like characteristics. If the phases (Φ_(nk) C_(n)) ofeach chip are uniquely determined, repeatable and synchronized to theMaster Clock (as shown in FIG. 2A), the transmitted waveform, W, can beclassified as pseudo-random noise. Such pseudo-random noise waveformsare coherent permitting implementation of coherent receivers.

Image processing advantages of wide instantaneous bandwidth,pseudo-random noise waveforms can include reduction, with properwaveform selection, and potential elimination of speckle, e.g.,speckles/speckle patterns, which are random intensity patterns producedby the mutual interference waveforms, which are commonly associated withconventional medical ultrasound images. This exemplary reduction inspeckle can be an analogous comparison of a scene illuminated by wideband, Gaussian noise-like white light, which has no observable speckleto narrow band laser illumination with exhibits strong speckle of thesame scene.

Signal processing advantages of coherent, pseudo-random noise,frequency- and phase-coded waveforms can include waveforms having verylow time and Doppler sidelobes. For example, an ambiguity function,A(τ,υ), can be a two-dimensional representation that shows thedistortion of a received waveform processed by a matched filter in thereceiver due to the effect of Doppler shift (υ) or propagation delay(τ). Specifically, the exemplary ambiguity function A(τ,υ) is defined byEquation (2) and is determined solely by the waveform properties and thereceiver characteristics and not by the scenario. The ambiguity functionof A(τ,υ) is defined by

$\begin{matrix}{{{A\left( {\tau,\upsilon} \right)} = {\int_{- \infty}^{+ \infty}{{X_{a}(t)}{X_{b}^{*}\left( {t - \tau} \right)}e^{j\; 2\;\pi\;\upsilon\; t}}}}\ } & (2)\end{matrix}$where

${{X_{k}(t)} = {\frac{1}{\sqrt{T}}e^{j{\lbrack{{2\;\pi\;{f_{k}{({t - t_{k}})}}} + \Phi_{k}}\rbrack}}}},{{{for}\mspace{14mu} 0} \leq t \leq T},{{X_{k}(t)} = 0}$otherwise.

For waveforms of the type described by Equation (1), the followingequation can be obtained:

$\begin{matrix}{{A\left( {\tau,\upsilon,t,f_{n},\Phi_{n},f_{m},\Phi_{m},T} \right)} = {\left( {1 - \frac{{\tau - \left( {\Delta\; t} \right)}}{T}} \right)\frac{{Sin}\left\lbrack {2{\pi\left( {\Delta\; f} \right)}\left( {T - {{\Delta\; t}}} \right)} \right\rbrack}{\left\lbrack {2{\pi\left( {\Delta\; f} \right)}\left( {t - {{\Delta\; t}}} \right)} \right\rbrack}e^{j\; 2{\pi{\lbrack{{\Delta\;{f{({T + {\Delta\; t}})}}} - {f_{n}\Delta\; t} + {\upsilon\; t} + {\Delta\;\Phi}}\rbrack}}}}} & (3)\end{matrix}$where Δt=τ−t, Δf=υ−(f_(n)−f_(m)), and ΔΦ=Φ_(n)−Φ_(m), which can resultin the complete ambiguity equation shown in Equation (4):

$\begin{matrix}{{x\left( {\tau,\upsilon} \right)} = {\frac{1}{M}{\sum\limits_{n}{\sum\limits_{m}{A\left( {\tau,\upsilon,t,f_{n},\Phi_{n},f_{m},\Phi_{m},T} \right)}}}}} & (4)\end{matrix}$where both n and m are a sequence of positive integers from N−M+1 to N.

FIG. 4 shows exemplary ambiguity function characteristics of apseudo-random noise, frequency-coded, composite waveform 401,represented by Equation (1) for waveform, W. The exemplaryfrequency-coded, composite waveform 401 includes a code length of 128.As shown in FIG. 4, the sidelobes 402 of this ambiguity function are dueto chip-to-chip phase interactions and have a plateau level in bothdelay and frequency below the peak that is a function of N².

By inspection, many composite waveforms (W) are possible depending onthe specific codes (I_(nk)) selected. However, the sidelobe performancecannot be guaranteed for every waveform defined, and therefore onlythose codes which give sufficiently low sidelobes in both delay andfrequency as determined by a numerical search of a set of possible codesshould be used.

For example, in medical ultrasound applications, living tissue as apropagation medium is inhomogeneous. Propagation medium inhomogeneitycan introduce differential time delays, and living tissue can introduceunwanted motion induced Doppler. Ultrasound transducer arrays also canhave undesirable side lobes and grating lobes (e.g., due to physicalsize limitations) in the off-axis portions of ultrasound beam that addunwanted time delay and Doppler returns to the returns of the main lobe.Waveforms that exhibit low ambiguity function sidelobes cansignificantly improve SAU focusing and target contrast due through thereduction interference from differential time delays, motion-inducedDoppler, and transducer side lobe effects.

Coherent pseudo-random noise, frequency- and/or phase-coded waveformscan enable higher-order cross-range focusing techniques to be employedthat can improve the lateral resolution of size limited ultrasoundtransducer arrays, e.g., medical ultrasound transducer arrays.

For example, each biological tissue type and each diseased tissue typemay exhibit their own unique ultrasound echo return signals as afunction of frequency, mono-static and bi-static angles, and spatialmorphology. Using conventional Elastograph-Mode (E-Mode) modalities, itcan be difficult to take advantage of such properties to classifytissues, e.g., due to measurement errors such as the inability toaccurately characterize the ultrasound wave propagation throughoverlaying inhomogeneous media. Exemplary waveforms produced by theexemplary SAU System 200, e.g., wide instantaneous bandwidth, coherentpseudo-random noise, frequency- and/or phase-coded waveforms, can enabletissue differentiation by determining the physical tissue features fromthe echo returns of the target volume under investigation. Classifiers,one example being Bayesian-inference classifiers among others, can beapplied to the feature data obtained from the measured characteristicsof the received echo to automatically classify tissue types observed inthe target volume providing a Computer Aided Diagnostic-Mode (CAD-Mode).

Unlike conventional E-Modes, which inherently have significantly reducedimage quality and rely on individual operator technique, the exemplarywaveforms described by Equation (1) can inherently provide improvedimage quality while simultaneously colorizing the resultant image bytissue type in the ATS and/or CAD-Modes. With this advantage, usertechnique can be mitigated and the margins of a lesion are discernible,thus permitting improved diagnoses.

In addition, the Waveform Synthesizers 208 positioned on transmit andthe Digital Signal Processor 204 positioned on receive (as shown in FIG.2A), can also perform beam control (e.g., beam steering, dynamic beamfocusing, and beamforming) functions. FIGS. 5A-5C show the basics ofthese digital electronic functions by introducing a differential timedelay, or equivalently a phase shift, and amplitude weighting betweeneach of the elements of the phased array. As can be seen in FIG. 5A, thedifferential phase shift can compensate for the differential change indistance (d) each acoustic ray (r₁, r₂, . . . r_(i) . . . ) travels fromi^(th) element to the point of focus (p). An angle (θ) is formed as thepoint of focus (p) is not along the z-axis direction of directaim/alignment of the Transducer Array 211 toward a target in the targetmedium. Additionally, a differential amplitude weight can be applied toeach element to control the beam shape and suppress side and gratinglobes. Also, for one or more chips in an exemplary waveform, theWaveform Generator 207 can pre-encode a phase delay to delay the phaseof the one or more chips transmitted at each transducer element in theTransducer Array 211. An exemplary result of this feature can be seen inFIGS. 5B and 5C. The exemplary phase delay values for the one or morechips can be communicated to the Digital Signal Processor 204 and/or theSystem Controller 202 to incorporate the phase delay values in thesignal processing of the received composite waveform.

For narrow instantaneous bandwidth ultrasound devices, this function canbe accomplished by introducing phase shift and amplitude attenuation onthe composite analog signal driving each element. However, for theexemplary spread-spectrum, wide instantaneous bandwidth, frequency- andphase-coded waveforms generated by the SAU System 200, each individualchip of the waveform (W_(i)) is individually amplitude weighted (B_(ni))and phase weighted (D_(ni)) as a function of frequency (n) for eacharray element (i) individually for all X elements, as indicated byEquation (5).

$\begin{matrix}{{W_{i}(t)} = {\sum\limits_{k}{\sum\limits_{n}{A_{n}B_{ni}e^{j{({{2\;\pi\;{nf}_{0}t} + \Phi_{nk} + C_{n} + D_{ni}})}}{U\left( {t - {kT}_{f}} \right)}}}}} & (5)\end{matrix}$

On transmit, the amplitude and phase weighting required of each chip canbe computed by the System Controller 202 and can be sent as aninstruction to the Waveform Generator 207. The Waveform Generator 207can then send the digital words (real and imaginary components) to theWaveform Synthesizers and the Beam Controller 208 that produces theanalog drive signal that is amplified by Amplifier 209 and sent to eachelement of the array of the Transducer Array 211.

Synthetic aperture ultrasound signal processing includes collecting thereceived synthetic aperture ultrasound signal data and processing thesedata by using a sequence of algorithms that utilizes a replica of thetransmitted waveform to produce a synthetic aperture ultrasound image.For example, the synthetic aperture ultrasound signal processing of thedisclosed technology negates the propagation effects of livinginhomogeneous tissue, e.g., by taking advantage of the “thumb-tack”ambiguity function, as shown in FIG. 4. On receive, the A/D Convertermodule 213 can convert the received analog signal to digital words. TheA/D Converter module 213 can send the digital words that represent theamplitude and phase information of each chip for each sampled positionof the real array element for each array element to the Digital SignalProcessor 204, where the data is collected and stored over the entiresynthetic aperture.

The axial resolution (∂_(a)) of a synthetic aperture waveform is givenby the expression ∂_(a)=c/B, where B is the bandwidth of the waveformand c is the speed of sound. The lateral resolution (∂₁) of a realaperture can be approximated by the expression ∂₁=dλ_(c)/w_(R). Thelateral resolution for a synthetic aperture, e.g., formed by the SAUSystem 200, can be approximated by ∂₁=dλ_(c)/2W, where λ_(c) is thewavelength of the center frequency of the transmitted waveform.

FIG. 6 shows a block diagram of an exemplary synthetic apertureultrasound signal processing technique 600 using digital signalprocessing to produce an ultrasound image. The technique can beimplemented to process exemplary coherent, wideband, instantaneous,spread-spectrum, coded, and noise-like ultrasound waveforms. Theexemplary synthetic aperture ultrasound signal processing technique canbe implemented using the Digital Signal Processor 204 of the SAU System200 for the exemplary SASS and SASpl modes, as shown in FIGS. 2C and 2D,respectively. As shown in FIG. 6, the SAU signal processing technique600 includes a process 610 to store the digital words that represent theamplitude and phase information of each frequency chip of thetransmitted ultrasound pulse and the returned echo signals for eachsampled position in a memory unit of the SAU System 200. In someimplementations, for example, the SAU signal processing technique 600can include a process 620 to performing axial range compression beforethe formation of the synthetic aperture, e.g., which can include thebenefit of conserving memory. The SAU signal processing technique 600can include a process 630 to form the synthetic aperture image byprocessing the stored block of axial-range compressed echo-data thatencompass the entire synthetic aperture. The SAU signal processingtechnique 600 can include a process 640 to process the SA image data toform an ultrasound image for display.

FIG. 7 shows a diagram of exemplary synthetic aperture-sampled receivedecho data and storage to memory. In this exemplary SAU data collectionscenario, the transducer sub-array phase center, which may be referredto simply as a probe, is translated either mechanically, orelectronically as portion of a larger array, in the SA coordinate systemshown along an arbitrary, but known, open or closed 3D path, in thegeneral case, sampling raw echo-return data at each u,v,w data point,and for each θ, φ beam angle. The digitized received-echo data for eachsample point and its 3D position are stored in a block of memory foreach complete scan. As shown in the process 610 of FIG. 6, the received,digitized, echo returns are collected and stored in memory. FIG. 7 showsa conceptual diagram of an exemplary synthetic aperture received datamemory map of the stored blocks of data. The collected digitizedreceived-echo data can be processed as a block of data on ablock-by-block basis.

The process 620 to perform axial range compression, e.g., using theDigital Signal Processor 204 of the SAU System 200, can be implementedaccording to the following example. FIG. 8 shows a block diagram of anexemplary wave-number algorithm for wideband, spread-spectrum,noise-like, coherent synthetic aperture image formation. In thisexample, the received signal, Y_(i)(τ,υ), for each data collectionsample point, can be multiplied by the complex conjugate replica of thetransmitted digital waveform, W_(i)*(τ) that is shifted in time t₀. Thismultiplication operation can be repeated J times, e.g., typically inparallel; but for each operation, the waveform replica is shifted intime by an integral increment, j·t₀, from the previous one, as shown inFIG. 8, and stored in memory based on the sampled data point in theexemplary memory map, as shown in FIG. 7. This step is repeated for eachof the sampled data points, producing the compressed axial-range datafor the axial-range slices, j, shown in the FIGS. 2C and 2D.

The process 630 to form the synthetic aperture image, e.g., using theDigital Signal Processor 204 of the SAU System 200, can be implementedusing any of several different sets of algorithms. For example, thesesets of synthetic aperture algorithms may be classified as eitherfrequency domain algorithms or as time domain algorithms. For example,types of frequency-domain algorithms can include wave-number algorithms,chirp-scaling algorithms, and scaled inverse-Fourier-transformalgorithms, among others. For example, types of time-domain algorithmscan include explicit matched-filter algorithms, and back-projectionalgorithms, among others. While all of these exemplary algorithms areapplicable to forming synthetic aperture coherent, wide instantaneousbandwidth, spread-spectrum, medical ultrasound images, the frequencydomain wave-number algorithm is provided as an example shown in FIG. 8,e.g., as the wave-number algorithm may be conceptually the easiest tounderstand.

The process 630 can include a window-filtering step of the producedcompressed axial-range data, as shown in FIG. 8. For example, tominimize spectral leakage due to the discontinuities at the extremitiesof finite-duration signal records, window-function filtering can beapplied to improve image quality. In this example, for each axial-rangeslice j, the resultant products are multiplied by a window function,e.g., such as a rectangular, Hann, Hamming, Tukey, Kaiser Bessel,Dolph-Chebyshev, Blackman-Harris, etc. window. These exemplary windowfunctions are tapered to zero at the extremities. The selection of awindow function may involve a tradeoff between the suppression ofspectral-leakage-induced image sidelobes and image resolution. Forexample, the more smoothly the window tapers to zero, the lower are theunwanted image sidelobes at the expense of reduced resolution.Conversely, for example, the ‘steeper’ the function goes to zero at theextremities, the sharper is the resolution at the expense of higherimage sidelobes. In one example, a rectangular window function canproduce the highest resolution and the highest sidelobes. Alternatively,for example, a Blackman-Harris window function can produce very lowsidelobes (e.g. below −70 dB) and lower resolution, e.g., as compared torectangular window functions. In the process 630, the selection of thespecific window function or functions to be implemented may be left tothe operator to the operator of the SAU System 200, e.g., since it isexamination-dependent.

The process 630 can include a Fourier Transform step of thewindow-function filtered data, as shown in FIG. 8. In some examples, atwo-dimensional, Discrete Fourier Transform (DFT) can be applied to ablock of digitized, range-compressed, received-echo data that waspreviously collected and stored in memory for the entire syntheticaperture. There are many alternative discrete Fourier transformalgorithms available for use in the process. Of the exemplary DFT class,a Cooley-Tukey algorithm can be implemented, albeit any of the DFT maysuffice. In the process 630, the selection of the Fourier Transformalgorithm to be implemented may be left to the operator to the operatorof the SAU System 200.

The process 630 can include a Stolt Transform step subsequent to theFourier Transform step, as shown in FIG. 8. The Stolt Transform can beused for lateral compression of the Fourier-transformed data collectedover the total synthetic aperture. For example, the wave-numberalgorithm basically inverts the imaging system data through a coordinatetransformation (Stolt Mapping) through interpolation in the spatialfrequency domain. The compressed-echo data, which was converted to thewavenumber domain in the Fourier Transform step, has a matched filteringapplied with respect to a target at a synthetic focus range, followed bya coordinate transformation in one step. The Stolt Transform convertsthe multiple polar data-set samples collected at each point, U, alongthe synthetic aperture, as illustrated in FIGS. 1B and 2D, to a singleimage, mapping it to a new X-Y coordinate system, focused at the origin,as shown in FIG. 9.

FIG. 9 shows a diagram illustrating an exemplary implementation of theStolt Transform process, which converts the multiple-sample image thatwere collected over the synthetic aperture from polar coordinates to onehigher-resolution image in a new coordinate system with an origin at thedesired point of focus. For illustrative purposes, it is assumed thatthe synthetic aperture in this example includes a one-dimensionaltransducer probe translating along the U axis. Following usualconvention, the temporal wavenumber is defined as K=2πf/c in thedirection of propagation. The spatial wavenumber is defined as K_(U)=Ksin Φ, where the angle Φ is given by the following expression:Φ=sin⁻¹(Y/√{square root over (X ² +Y ²)}),  (6)which is centered (e.g., focused) on the origin of the X-Y coordinatesystem. The spatial wavenumbers K_(X) and K_(Y) are in the direction ofthe X and Y axes respectively. For this specific example of the geometryshown in FIG. 9, the Stolt mapping is the following:K _(X)(f,K _(U))=√{square root over (4K ² −K _(U) ²)}K _(Y)(f,K _(U))=K _(U)  (7)

The process 630 can include an Inverse Fourier Transform step subsequentto the Stolt Transform step, as shown in FIG. 8. A two-dimensional,inverse Discrete Fourier Transform can be applied to the results fromthe previous Stolt Transform step. For example, since the inverse DFT isessentially the same algorithm as the DFT, except for a 1/N factor andan opposite sign in the exponent, like the DFT there are manyalternative inverse DFTs that are available for implementation of thisstep. For example, a commonly used DFT includes the Cooley-Tukeyalgorithm, but since any of the DFT algorithms can be implemented, butany of the inverse DFT algorithms may suffice. In the process 630, theselection of the Inverse Fourier Transform algorithm to be implementedmay be left to the operator to the operator of the SAU System 200.

In some implementations of the process 630, for example, an autofocusingstep may be performed. For example, the focusing of a synthetic apertureopen-loop formed image may optionally be improved using any number ofwell-known Synthetic Aperture Radar (SAR) and Synthetic Aperture Sonar(SAS) autofocus algorithms that lower the sidelobes of Point SpreadFunction (PSF) of the resultant image. Since the received syntheticaperture data is block-processed, those portions of the image away fromthe point of focus may be imperfectly focused, due to arbitrary phaseerrors. Implementing one or more autofocus techniques may at leastpartially correct to improve image quality.

In synthetic aperture image formation, open-loop synthetic aperturedigital processing algorithms, such as those described previously, canassume medium homogeneity, stationarity, and precisetransmit-and-receive transducer-sampling locations with respect to thescene. For example, the desired level of homogeneity, stationarity andtransducer location may not be completely realizable with livingmammalian subjects. Therefore, in some exemplary implementations, it maybe desirable to form the synthetic aperture image by applying a set ofopen-loop synthetic aperture algorithms and then apply a global or aseries of regional autofocus algorithms taking advantage of thecoherent, spread-spectrum nature of the waveforms to improve imagequality by lowering the sidelobes of the PSF that are not coherent fromaperture sampling point to sampling point. For example, open-loopsynthetic aperture algorithms use the best available estimates fortransducer sample locations and tissue parameters using the bestavailable estimates for transducer sample locations and tissueparameters, then the autofocus algorithm searches for optimal imagequality to refine the image formation parameters, e.g., mitigatingestimate imprecision in transducer location, inhomogeneous tissuecharacteristics, and incoherent PSF sidelobes. Since autofocustechniques rely on coherency and redundancy in the raw data, thereceived-echo signal preferably can be over-sampled both temporally andspatially than the Nyquist limit, e.g., if significant improvement inimage quality is to be realized. For example, the temporal samplinginterval can be less than 1/(2Nf₀), and the spatial sampling intervalcan be less than a half wavelength at mid-frequency or c/[(N+M)f₀].

FIG. 10 shows a block diagram of an exemplary coherent, iterative,closed-loop, synthetic aperture image autofocus subroutine. Theexemplary coherent, iterative, closed-loop, autofocus image correctionprocess can be implemented to improve the quality of the imagecompensation for undesirable variations in axial-lateral syntheticaperture phase history, but at the expense of additional digitalsignal-processing load.

In the exemplary iterative, closed-loop, synthetic aperture imageautofocus subroutine of FIG. 10, first, the phase error based on the rawreceived-echo data is estimated, and then the estimated/incoherent phaseerrors in these data are removed. For example, depending on the natureand magnitude of the phase errors, they can significantly degrade theimage quality in terms of geometry, resolution, contrast and reducedsignal-to-noise ratio (SNR), as shown in Table 1, which shows the effectof various types of phase errors on reconstructed images.

TABLE 1 Phase Error Variation over Entire Synthetic Type of ErrorAperture Effect on Image Slowly Varying Linear Geometric (Affects MainLobe) Displacement Quadratic Defocus/Reduced Resolution Higher OrderDistortion Polynomial Rapidly Varying Sinusoidal Image Artifacts(Affects Side Lobes) Random Wideband Reduced Contrast & IncoherentNoiseSNR

While there are many well-known autofocus algorithms, they can begrouped, in general, into either non-parametric, or model-based, or acombination of the two types. For example, one commonly-usednon-parametric algorithms includes the phase-gradient algorithm, whichexhibits an ability to remove higher order phase errors over a varietyof scenes. In addition, there are several algorithms that have beendeveloped that are enhancements to the phase-gradient algorithm. Forexample, the eigenvector algorithm, which is a maximum-likelihoodestimator, and the weighted least-square algorithm that minimizes thevariance of the phase error, are two examples from among many.

Model-based, autofocus algorithms employ a model of the systematic,position-dependent, slowly varying, phase errors present in everyphysical measurement system. For example, a device-dependent, samplingposition error model is developed for the mechanical elements of thetransducer scanning assembly. Given such a model, the phase errors areestimated and phase error corrections are iterated until the best imageis obtained based on some predetermined quality metric.

One example of a hybrid non-parametric, model-based approach is tosegment the image into sub-images using an error model of the scanningsystem, such that the phase errors present on each sub-image areposition invariant. A non-parametric autofocus algorithm, e.g., such asthe phase-gradient algorithm, can then be applied individually to eachsub-image. Lastly, for example, the individual sub-images arereassembled together to form a complete autofocused image.

One of the advantages of the coherent, broadband waveform of Equation 5is that the received signal may be segmented into sub-bands and thelowest frequency (e.g., longest wavelength) sub-band may be selectedfirst for phase-error estimation. This longest wavelength sub-bandeffectively has the least impact of phase errors, e.g., due to theinhomogeneous tissue and sampling position uncertainties, as compared tothe higher frequency (shorter wavelength) sub-bands. Upon achieving apredefined level of image quality, e.g., by employing a selectedautofocus algorithm such as the phase gradient algorithm, selected andprogressively shorter wavelength sub-band data may be used for furtherrefine the estimate of the phase errors present, if desired. Lastly, forexample the phase-corrected sub-band data are reassembled to form acomplete autofocused image.

Several applications and uses of the disclosed technology can beimplemented to exploit the described features of the aforementionedsystems, methods, and devices. Some examples are described for clinicaluse of the disclosed technology.

In one exemplary application, the resultant image quality, and the ATSand CAD modes of an exemplary spread-spectrum ultrasound device canenable the primary care physician to incorporate this modality into aroutine examination screening protocol to locate early stagemalignancies (e.g., Stage 0 or 1), as well as later stage cancers. Asthe result of this application, the device can potentially, for example,enhance the survival rate of hard-to-diagnose asymptomatic patientssuffering from malignancies, e.g., such as stomach, pancreatic, bladdercancers, etc.

In another exemplary application, the resultant image quality, ATS andCAD modes of an exemplary spread-spectrum ultrasound device can permitboard-certified radiologists to diagnose neoplasms as benign ormalignant prior to any surgical biopsy or resection intervention. As aresult of this application, the ability of radiologists to locate anddiagnose early stage malignancies (e.g., Stage 0 or 1) can potentiallyimprove patient survival rate. Additionally, unnecessary biopsiespotentially can be avoided, along with their attendant risk ofhard-to-treat or even lethal complications such as, for example,methicillin-resistant Staphylococcus aureus (MRSA staph) infections.

In another exemplary application, the resultant 2D or 3D image qualityof an exemplary spread-spectrum ultrasound device and, optionally, its4D imaging capability (e.g., which can be derived from the sequentialstorage of 3D images) can be used in fine needle biopsy and othermedical procedures. For example, the exemplary spread-spectrumultrasound device can be integrated into an exemplary fine-needle biopsyinstrument (e.g., with the device's transducer probe), which can permitthe fine-needle biopsy of very small, early stage (e.g., Stage 0 or 1)neoplasms to confirm noninvasive diagnoses. As a result of thisapplication, the ability of surgeons to avoid open biopsies and thepotential for hard-to-treat and lethal complications that may result isclearly beneficial to the patient.

In another exemplary application, the integration of this device'sspread-spectrum transducer probe with minimally invasive surgical highdefinition video instrumentation can permit the fusing of the opticaland ultrasound images. Given the improved 2D or 3D image quality of thisspread-spectrum ultrasound device, optionally, its 4D imagingcapability, and the ATS and CAD modes, such fused video and ultrasoundimages can give surgeons the added ability to locate and surgicallyexcise diseased tissue without excising excessive healthy tissue.

In another exemplary application, the integration of this device'sspread-spectrum, 2D or 3D high-definition imaging mode of operation,with this device's HIFU minimally invasive mode of operation, can permitthe precision minimally invasive surgical therapeutic options. Given theimproved 2D or 3D image quality of this spread-spectrum ultrasounddevice, optionally, and its 4D imaging capability, and the ATS and CADmodes, such ultrasound images can give surgeons the added ability tolocate and surgically destroy diseased tissue with rapid heat elevationwithout destroying excessive healthy tissue.

In another exemplary application, given the improved 3D image quality ofthis spread-spectrum ultrasound device, optionally, its 4D imagingcapability, and the ATS modes, an exemplary spread-spectrum ultrasounddevice can reduce the amount of time for the brachytherapy treatment ofmalignant neoplasms by precisely guiding the insertion of catheters andsealed radioactive sources into the proper location. The application ofthis spread-spectrum ultrasound device to brachytherapy can beespecially useful for the treatment of small, hard-to-locate neoplasmsand their margins.

In another exemplary application, given the improved 3D image quality ofthis spread-spectrum ultrasound device, optionally, its 4D imagingcapability, and the ATS modes, an exemplary spread-spectrum ultrasounddevice can enable the effective insertion of high-dose, localizedpharmaceutical treatments of diseases by precisely guiding the insertionof catheters and pharmaceuticals into the proper location. Theapplication of this spread-spectrum ultrasound device to brachytherapycan be especially useful for the treatment of small, hard-to-locateneoplasms.

EXAMPLES

The following examples are illustrative of several embodiments of thepresent technology. Other exemplary embodiments of the presenttechnology may be presented prior to the following listed examples, orafter the following listed examples.

In one example of the present technology (example 1), a method ofproducing acoustic waveforms in an acoustic imaging device includessynthesizing, in one or more waveform synthesizers, one or morecomposite waveforms to be transmitted toward a target, in which acomposite waveform is formed of a plurality of individual orthogonalcoded waveforms that are mutually orthogonal to each other andcorrespond to different frequency bands, such that each of theindividual orthogonal coded waveforms includes a unique frequency with acorresponding phase; transmitting, from one or more transmittingpositions relative to the target, one or more composite acousticwaveforms including a plurality of acoustic waveforms, in which thetransmitting includes selecting one or more transducing elements of anarray to transduce the plurality of individual orthogonal codedwaveforms of the respective one or more composite waveforms into theplurality of corresponding acoustic waveforms of the respective one ormore composite acoustic waveforms; and receiving, at one or morereceiving positions relative to the target, returned acoustic waveformsthat are returned from at least part of the target corresponding to thetransmitted acoustic waveforms, in which the receiving includesselecting at least some of the transducing elements of the array toreceive the returned acoustic waveforms, in which the transmittingpositions and the receiving positions each include one or both ofspatial positions of an array of transducer elements relative to thetarget and beam phase center positions of the array, and in which thetransmitted acoustic waveforms and the returned acoustic waveformsproduce an enlarged effective aperture of the acoustic imaging device.

Example 2 includes the method of example 1, in which, in transmittingthe acoustic waveforms to the target, controlling the transducerelements of the array to cause the composite waveforms to change inorientation with respect to the target so that the target receives theacoustic waveforms at different waveform orientations over an imagingperiod.

Example 3 includes the method of example 2, in which the controlling thetransducer elements includes translating the array along the pluralityof spatial positions relative to the target to cause the change inorientation of the composite waveform with respect to the target.

Example 4 includes the method of example 2, in which the controlling thetransducer elements includes changing the beam phase center positions ofthe transmitted acoustic waveforms on the one or more transducerelements of the array to cause the change in orientation of thecomposite waveform with respect to the target.

Example 5 includes the method of example 1, in which each waveform ofthe plurality of individual orthogonal coded waveforms includes aplurality of amplitudes and a plurality of phases that are individuallyamplitude weighted and individually phase weighted, respectively.

Example 6 includes the method of example 1, in which the synthesizingthe individual orthogonal coded waveforms of the composite waveformincludes selecting the frequency bands, and determining one or moreamplitudes, a time-bandwidth product parameter, and a phase parameter ofeach individual orthogonal coded waveform.

Example 7 includes the method of example 6, in which the phase parameteris determined from a set of a pseudo-random numbers or from a set ofdeterministic numbers.

Example 8 includes the method of example 1, in which the transmittingthe plurality of the acoustic waveforms includes sequentially orsimultaneously transmitting the acoustic waveforms from at least oneposition of the plurality of positions.

Example 9 includes the method of example 1, in which the individualorthogonal coded waveforms include coherent waveforms.

Example 10 includes the method of example 1, further including forming aradio frequency (RF) waveform based on the composite waveform, in whichin the transmitted acoustic waveforms are generated by transducing theRF-based composite waveform at the one or more transducer elements ofthe array.

Example 11 includes the method of example 10, further includingamplifying the RF-based composite waveform.

Example 12 includes the method of example 1, further includingamplifying the received returned acoustic waveforms.

Example 13 includes the method of example 1, further includingconverting the received returned acoustic waveforms from analog formatto digital format as one or more received composite waveformscorresponding to the one or more composite waveforms, each receivedcomposite waveform including information of the target, in which theinformation includes an amplitude and a phase associated with thecorresponding frequency bands of the received composite waveform.

Example 14 includes the method of example 13, in which at least one ofthe amplitude or the phase is individually amplitude weighted or phaseweighted, respectively, for at least one frequency band of thecorresponding frequency bands of the received composite waveform.

Example 15 includes the method of example 1, further includingprocessing the received returned acoustic waveforms to produce an imageof at least part of the target.

Example 16 includes the method of example 15, further includingconverting the received returned acoustic waveforms from analog formatto digital format as one or more received composite waveformscorresponding to the one or more composite waveforms, each receivedcomposite waveform including information of the target; and storing theone or more composite waveforms and the corresponding one or morereceived composite waveforms in a memory map of data blocks, in whicheach data block stores the received returned acoustic waveform of thecomposite waveform for each sample point, the corresponding individualorthogonal coded waveform, and corresponding position data of the one ormore transducer elements for the sample point.

Example 17 includes the method of example 15, in which the processingincludes performing axial range compression of the stored receivedcomposite waveforms; and forming a synthetic aperture image byprocessing each stored block of axial-range compressed data thatencompass the effective aperture using one or more frequency- ortime-domain processing techniques.

In one example of the present technology (example 18), a syntheticaperture acoustic waveform imaging system includes a waveform generationunit including one or more waveform synthesizers coupled to a waveformgenerator, in which the waveform generation unit synthesizes a compositewaveform including a plurality of individual orthogonal coded waveformscorresponding to different frequency bands that are generated by the oneor more waveform synthesizers according to waveform information providedby the waveform generator, in which the individual orthogonal codedwaveforms are mutually orthogonal to each other and correspond todifferent frequency bands, such that each of the individual orthogonalcoded waveforms includes a unique frequency with a corresponding phase;a transmit/receive switching unit that switches between a transmit modeand a receive mode; an array of transducer elements in communicationwith the transmit/receive switching unit to transmit a compositeacoustic waveform including a plurality of acoustic waveforms from oneor more transmitting positions relative to the target, the transmittedacoustic waveforms of the composite acoustic waveform based on thesynthesized individual orthogonal coded waveforms of the compositewaveform, and to receive at one or more receiving positions relative tothe target returned acoustic waveforms corresponding to the plurality oftransmitted acoustic waveforms that return from at least part of thetarget, in which the transmitted acoustic waveforms and the returnedacoustic waveforms produce an enlarged effective aperture of thesynthetic aperture acoustic waveform imaging system, and in which thetransmitting positions and the receiving positions each include one orboth of spatial positions and beam phase center positions; amultiplexing unit in communication with the array of transducer elementsto select one or more transducing elements of an array to transduce theplurality of individual orthogonal coded waveforms into the plurality ofcorresponding acoustic waveforms, and to select one or more transducingelements of the array to receive the returned acoustic waveforms; anarray of analog to digital (A/D) converters to convert the receivedreturned acoustic waveforms that are received by the array of transducerelements from analog format to digital format, in which the receivedreturned acoustic waveforms provide information of the target; acontroller unit in communication with the waveform generation unit andthe array of A/D converters, the controller unit including a memory unitto store data and a processing unit coupled to the memory unit toprocess the information as data; and a user interface unit incommunication with the controller unit.

Example 19 includes the system of example 18, in which the stored dataincludes the digital format of the received returned acoustic waveforms,the corresponding synthesized composite waveform, and correspondingposition data of the array of transducers elements in the one or moretransmitting and receiving positions.

Example 20 includes the system of example 18, in which the waveformgeneration unit further includes one or more amplifiers, configuredbetween the transmit/receive switching unit and the one or more waveformsynthesizers, which modifies the composite waveform.

Example 21 includes the system of example 18, further including an arrayof one or more pre-amplifiers, configured between the transmit/receiveswitching unit and the array of A/D converters, which modifies thereceived returned acoustic waveform.

Example 22 includes the system of example 18, in which the processingunit includes a digital signal processor.

Example 23 includes the system of example 18, in which the controllerunit further includes a master clock that synchronizes time in at leastone of the elements of the acoustic waveform imaging system.

Example 24 includes the system of example 18, in which the controllerunit is configured to process the information to produce an image of atleast part of the target.

Example 25 includes the system of example 18, in which the userinterface unit includes a display that displays the image and a userinput terminal to receive user input data including a mode of operationfor operation of the system.

Example 26 includes the system of example 25, in which the mode ofoperation includes at least one of ATS-Mode (Artificial Tissue StainingMode) for imaging biological tissue that enables image color codingbased on at least one feature of one or more measured properties thatare obtained from the returned acoustic waveform.

Example 27 includes the system of example 25, in which the mode ofoperation includes at least one of CAD-Mode (Computer Aided DiagnosticMode) for imaging biological tissue that uses one or more algorithmicclassifiers to classify biological tissue types using at least onefeature of one or more measured properties that are obtained from thereturned acoustic waveform.

Example 28 includes the system of example 25, in which the display isconfigured to display a color coded image of the biological tissue basedon the classified biological tissue types.

Example 29 includes the system of example 18, in which, in transmittingthe acoustic waveforms to the target, the controller unit is configuredto control the array of transducer elements to cause the compositewaveform to change in orientation with respect to the target so that thetarget receives the composite acoustic waveform with different waveformorientations over an imaging period.

Example 30 includes the system of example 18, in which the array oftransducer elements is operable for moving in one dimension, twodimensions, or three dimensions along the transmitting positions totransmit the plurality of acoustic waveforms and along the receivingpositions to receive the returned acoustic waveforms.

Example 31 includes the system of example 18, in which at least one ofthe transducer elements of the array is capable of moving separately inthe one dimension, two dimensions, or three dimensions from the othertransducer elements of the transmitter array.

In one example of the present technology (example 32), a method ofcreating an image from an acoustic waveform includes combining aplurality of coded waveforms corresponding to different frequency bandsto produce a composite waveform including individual orthogonal wavesignals at the different frequency bands, in which the coded waveformsinclude a unique frequency with a corresponding phase and amplitude;producing an acoustic wave using the composite waveform for transmissiontoward a target from a first spatial position relative to the target, inwhich the acoustic wave includes individual acoustic wave signalscorresponding to the coded waveforms of the composite waveform;transmitting the acoustic wave to the target, in which the individualacoustic wave signals vary in orientation with respect to each other sothat the target receives the individual acoustic wave signals withdifferent waveform orientations over an imaging period; receivingreturned acoustic signals from at least part of the target after thetransmitted acoustic wave is sent to the target; repeating the combiningstep, the producing step, and the transmitting step from at least asecond position relative to the target, in which the combining,producing, and transmitting steps are repeated for plurality ofpositions to form a synthetic aperture; converting the received returnedacoustic signals from the plurality of positions into correspondingdigital composite waveforms each including information of the target;and processing the received composite waveforms to produce an image ofat least part of the target.

Example 33 includes the method of example 32, further includingprocessing the received composite waveforms in real time to produce asynthetic aperture image.

Example 34 includes the method of example 33, further including steeringa direction of the transmitted acoustic waves, based on the producedsynthetic aperture image, at one or more positions of the plurality ofpositions in a direct path toward the target.

In one example of the present technology (example 35), a method ofcreating an image from an acoustic waveform includes combining aplurality of coded waveforms corresponding to different frequency bandsto produce a composite waveform including individual orthogonal wavesignals at the different frequency bands, in which the coded waveformsinclude a unique frequency with a corresponding phase and amplitude;producing an acoustic wave formed of individual acoustic wave signalscorresponding to the coded waveforms of the composite waveform fortransmission toward a target; transmitting the acoustic wave to thetarget, in which the individual acoustic wave signals are transmittedfrom a first set of beam phase center positions at one or more spatialpositions relative to the target, and in which the individual acousticwave signals vary in orientation with respect to each other so that thetarget receives the individual acoustic wave signals with differentwaveform orientations over an imaging period; receiving returnedacoustic signals from at least part of the target after the transmittedacoustic wave is sent to the target; repeating the combining step, theproducing step, and the transmitting step from at least a second set ofbeam phase center positions relative to the target at the one or morespatial positions relative to the target, thereby forming a syntheticaperture; converting the received returned acoustic signals intocorresponding digital composite waveforms each including information ofthe target; and processing the received composite waveforms to producean image of at least part of the target.

Example 36 includes the method of example 35, further includingprocessing the received composite waveforms in real time to produce asynthetic aperture image.

Example 37 includes the method of example 36, further including steeringa direction the transmitted acoustic waves based on the producedsynthetic aperture image.

In one example of the present technology (example 38), a syntheticaperture acoustic waveform imaging system includes a waveform generationunit including one or more waveform synthesizers coupled to a waveformgenerator, in which the waveform generation unit synthesizes a compositewaveform including a plurality of individual orthogonal coded waveformscorresponding to different frequency bands that are generated by the oneor more waveform synthesizers according to waveform information providedby the waveform generator, in which the individual orthogonal codedwaveforms are mutually orthogonal to each other and correspond todifferent frequency bands, such that each of the individual orthogonalcoded waveforms includes a unique frequency with a corresponding phase;a transmitter array of transducer elements in communication with thewaveform generation unit to transmit a composite acoustic waveformincluding a plurality of acoustic waveforms from one or moretransmitting positions relative to the target, the transmitted acousticwaveforms of the composite acoustic waveform based on the synthesizedindividual orthogonal coded waveforms of the composite waveform, inwhich the transmitting positions include one or both of spatialpositions of the transmitter array and beam phase center positions ofthe transducer elements of the transmitter array; a receiver array oftransducer elements in communication with the waveform generation unitto receive at one or more receiving positions relative to the targetreturned acoustic waveforms corresponding to the transmitted acousticwaveforms that return from at least part of the target, in which thetransmitted acoustic waveforms and received acoustic waveforms producean enlarged effective aperture of the synthetic aperture acousticwaveform imaging system, and in which the transmitting positions and thereceiving positions each include one or both of spatial positions andbeam phase center positions; a first multiplexing unit and a secondmultiplexing unit in communication with the transmitter array andreceiver array, respectively, to select one or more of the transducingelements of the transmitter array to transduce the plurality ofindividual orthogonal coded waveforms into the plurality ofcorresponding acoustic waveforms, and to select one or more transducingelements of the receiver array to receive the returned acousticwaveforms; an array of analog to digital (A/D) converters to convert thereceived returned acoustic waveforms that are received by the receiverarray of transducer elements from analog format to digital format, inwhich the received returned acoustic waveforms provide information ofthe target; a controller unit in communication with the waveformgeneration unit and the array of A/D converters, the controller unitincluding a memory unit to store data and a processing unit coupled tothe memory unit to process the information as data; and a user interfaceunit in communication with the controller unit.

Example 39 includes the system of example 38, in which the stored dataincludes the digital format of the received returned acoustic waveforms,the corresponding synthesized composite waveform, and correspondingposition data of the transmitter array and the receiver array in the oneor more transmitting and receiving positions, respectively.

Example 40 includes the system of example 38, in which the waveformgeneration unit further includes one or more amplifiers, configuredbetween the transmit/receive switching unit and the one or more waveformsynthesizers, which modifies the composite waveform.

Example 41 includes the system of example 38, further including an arrayof one or more pre-amplifiers, configured between the receiving arrayand the array of A/D converters, which modifies the received returnedacoustic waveform.

Example 42 includes the system of example 38, in which the processingunit includes a digital signal processor.

Example 43 includes the system of example 38, in which the controllerunit further includes a master clock that synchronizes time in at leastone of the elements of the acoustic waveform imaging system.

Example 44 includes the system of example 38, in which the controllerunit is configured to process the information to produce an image of atleast part of the target.

Example 45 includes the system of example 38, in which the userinterface unit includes a display that displays the image and a userinput terminal to receive user input data including a mode of operationfor operation of the system.

Example 46 includes the system of example 45, in which the mode ofoperation includes at least one of ATS-Mode (Artificial Tissue StainingMode) for imaging biological tissue that enables image color codingbased on at least one feature of one or more measured properties thatare obtained from the returned acoustic waveform.

Example 47 includes the system of example 45, in which the mode ofoperation includes at least one of CAD-Mode (Computer Aided DiagnosticMode) for imaging biological tissue that uses one or more algorithmicclassifiers to classify biological tissue types using at least onefeature of one or more measured properties that are obtained from thereturned acoustic waveform.

Example 48 includes the system of example 45, in which the display isconfigured to display a color coded image of the biological tissue basedon the classified biological tissue types.

Example 49 includes the system of example 38, in which, in transmittingthe acoustic waveforms to the target, the controller unit is configuredto control the transmitter array to cause the composite waveform tochange in orientation with respect to the target so that the targetreceives the composite acoustic waveform with different waveformorientations over an imaging period.

Example 50 includes the system of example 38, in which the transmitterarray of transducer elements is operable for moving in one dimension,two dimensions, or three dimensions along the plurality of positions totransmit the plurality of acoustic waveforms.

Example 51 includes the system of example 38, in which one or moretransducer elements of the transmitter array is capable of movingseparately in the one dimension, two dimensions, or three dimensionsfrom the other transducer elements of the transmitter array.

Example 52 includes the system of example 38, in which the receiverarray of transducer elements is operable for moving in one dimension,two dimensions, or three dimensions along the plurality of positions toreceive the returned acoustic waveforms.

Example 53 includes the system of example 38, in which one or moretransducer elements of the receiver array is capable of movingseparately in the one dimension, two dimensions, or three dimensionsfrom the other transducer elements of the transmitter array.

Example 54 includes the system of example 38, in which the number oftransducer elements of the transmitter array is greater than the numberof transducer elements of the receiver array.

Implementations of the subject matter and the functional operationsdescribed in this specification, such as various modules, can beimplemented in digital electronic circuitry, or in computer software,firmware, or hardware, including the structures disclosed in thisspecification and their structural equivalents, or in combinations ofone or more of them. Implementations of the subject matter described inthis specification can be implemented as one or more computer programproducts, e.g., one or more modules of computer program instructionsencoded on a tangible and non-transitory computer-readable medium forexecution by, or to control the operation of, data processing apparatus.The computer-readable medium can be a machine-readable storage device, amachine-readable storage substrate, a memory device, a composition ofmatter affecting a machine-readable propagated signal, or a combinationof one or more of them. The term “data processing apparatus” encompassesall apparatus, devices, and machines for processing data, including byway of example a programmable processor, a computer, or multipleprocessors or computers. The apparatus can include, in addition tohardware, code that creates an execution environment for the computerprogram in question, e.g., code that constitutes processor firmware, aprotocol stack, a database management system, an operating system, or acombination of one or more of them.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, and it can bedeployed in any form, including as a stand-alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program can be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub programs, or portions of code). A computer programcan be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this specification can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special-purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special-purpose microprocessors, suchas, for example, digital signal processors (DSP), and any one or moreprocessors of any kind of digital computer. Generally, a processor willreceive instructions and data from a read only memory or a random accessmemory or both. The essential elements of a computer are a processor forperforming instructions and one or more memory devices for storinginstructions and data. Generally, a computer will also include, or beoperatively coupled to receive data from or transfer data to, or both,one or more mass storage devices for storing data, e.g., magnetic,magneto optical disks, or optical disks. However, a computer need nothave such devices. Computer-readable media suitable for storing computerprogram instructions and data include all forms of non volatile memory,media and memory devices, including by way of example semiconductormemory devices, e.g., EPROM, EEPROM, and flash memory devices. Theprocessor and the memory can be supplemented by, or incorporated in,special-purpose logic circuitry.

While this patent document contains many specifics, these should not beconstrued as limitations on the scope of any invention or of what may beclaimed, but rather as descriptions of features that may be specific toparticular embodiments of particular inventions. Certain features thatare described in this patent document in the context of separateembodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various systemcomponents in the embodiments described above should not be understoodas requiring such separation in all embodiments.

Only a few implementations and examples are described and otherimplementations, enhancements and variations can be made based on whatis described and illustrated in this patent document.

What is claimed is:
 1. A method for synthetic aperture acoustic imaging,comprising: generating, by a waveform generator, a plurality ofindividual coded waveforms that correspond to different frequency bands,such that each of the individual coded waveforms includes a uniquefrequency with a corresponding phase; synthesizing, by one or morewaveform synthesizers, a first composite waveform and a second compositewaveform to be transmitted toward a target, wherein the first compositewaveform is formed of one or more of the individual coded waveforms andthe second composite waveform is formed of one or more of the individualcoded waveforms; selecting one or more transducer elements of an arrayof transducer elements to transduce the first composite waveform into afirst composite acoustic waveforms to be transmitted at a target; andselecting one or more additional transducer elements of an array oftransducer elements to transduce the second composite waveforms into asecond composite acoustic waveform to be transmitted at the target,wherein the first composite acoustic waveform and the second compositeacoustic waveform produce an enlarged non-real aperture when transmittedat the target.
 2. The method of claim 1, wherein the first compositewaveform is different than the second composite waveform.
 3. The methodof claim 1, wherein the selected transducer elements determine atransmitting position for each of the first composite acoustic waveformand the second composite acoustic waveform that includes one or both of(i) a spatial position of the array of transducer elements relative tothe target and (ii) a beam phase center position of the array oftransducer elements.
 4. The method of claim 1, comprising: adjusting aphase of the individual coded waveforms of one or both of the firstcomposite waveform and the second composite waveform so that one or bothof the first composite waveform and the second composite waveform appearto emanate from a virtual point source to approximate a point sourceradiator.
 5. The method of claim 1, comprising: adjusting a phase of theindividual coded waveforms of one or both of the first compositewaveform and the second composite waveform so that one or both of thefirst composite waveform and the second composite waveform appear toemanate from multiple phase centers.
 6. The method of claim 1, whereinthe first composite waveform includes two or more of the individualcoded waveforms, and the second composite waveform includes two or moreof the individual coded waveforms, the method comprising: adjusting asignal power between at least two different individual coded waveformsof the first composite waveform, and adjusting a signal power between atleast two different individual coded waveforms of the second compositewaveform, wherein the adjusting the signal power spreads acoustic powerof the first composite acoustic waveform and the second compositeacoustic waveform over a wide band.
 7. The method of claim 1, whereineach waveform of the plurality of individual coded waveforms includes aplurality of amplitudes and a plurality of phases that are individuallyamplitude weighted and individually phase weighted, respectively.
 8. Themethod of claim 1, wherein the individual coded waveforms are individualorthogonal coded waveforms that are mutually orthogonal to each other.9. The method of claim 1, wherein the individual coded waveforms includecoherent waveforms.
 10. The method of claim 1, wherein the generatingthe plurality of individual coded waveforms includes selecting thedifferent frequency bands, and determining one or more amplitudes, atime-bandwidth product parameter, and a phase parameter of eachindividual coded waveform.
 11. A synthetic aperture acoustic waveformimaging system, comprising: a waveform generation unit comprising one ormore waveform synthesizers coupled to a waveform generator, wherein thewaveform generation unit is operable to generate a composite waveformcomprising a plurality of individual coded waveforms corresponding todifferent frequency bands, wherein each individual coded waveform of theplurality of individual coded waveforms includes a unique frequency witha corresponding phase; an array of transducer elements in communicationwith the waveform generation unit to transduce the plurality ofindividual coded waveforms into a plurality of acoustic waveforms to betransmitted at a target, wherein an acoustic waveform corresponds to atransduced individual coded waveform; and a multiplexing unit incommunication with the array of transducer elements to select one ormore of the transducer elements of the array as a transducer segmentcorresponding to an individual acoustic waveform, wherein the transducersegment specifies a transmitting position that includes one or both of(i) a spatial position of the array of transducer elements relative tothe target and (ii) a beam phase center position of the array oftransducer elements, wherein the system is operable to transmit acomposite acoustic waveform comprising two or more acoustic waveformsfrom one or more known transmitting positions relative to the target toproduce a composite acoustic beam, and wherein a transmitted compositeacoustic waveform produces an enlarged non-real aperture.
 12. The systemof claim 11, wherein the system is operable to transmit the compositeacoustic waveform by sequentially transmitting the two or more acousticwaveforms from at least one position or simultaneously transmitting thetwo or more acoustic waveforms from at least two positions to producethe composite acoustic beam transmitted from the one or more knowntransmitting positions.
 13. The system of claim 11, comprising: an arrayof analog to digital (A/D) converters to convert received returnedacoustic waveforms that are received by the array of transducer elementsfrom analog format to digital format, wherein the received returnedacoustic waveforms provide information of the target; a controller unitin communication with the waveform generation unit and the array of A/Dconverters, the controller unit comprising a memory unit to store dataand a processing unit coupled to the memory unit to process theinformation as data; and a user interface unit in communication with thecontroller unit.
 14. The system of claim 11, wherein the system isconfigured to adjust a signal power between at least two differentindividual coded waveforms of the composite waveform, wherein adjustmentof the signal power spreads acoustic power of the transmitted compositeacoustic waveform over a wide band.
 15. The system of claim 11, whereinthe system is configured to adjust a phase of the individual codedwaveforms associated with the composite waveform so that the compositewaveform appears to emanate from a virtual point source to approximate apoint source radiator.
 16. The system of claim 11, wherein the system isconfigured to adjust a phase of the individual coded waveformsassociated with the composite waveform so that the composite waveformappears to emanate from multiple phase centers.
 17. The system of claim11, wherein each waveform of the plurality of individual coded waveformsincludes a plurality of amplitudes and a plurality of phases that areindividually amplitude weighted and individually phase weighted,respectively.
 18. The system of claim 11, wherein the individual codedwaveforms are individual orthogonal coded waveforms that are mutuallyorthogonal to each other.
 19. The system of claim 11, wherein theindividual coded waveforms include coherent waveforms.
 20. The system ofclaim 11, wherein the waveform generation unit, in generating theplurality of individual coded waveforms, is configured to select thedifferent frequency bands and determine one or more amplitudes, atime-bandwidth product parameter, and a phase parameter of eachindividual coded waveform.